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 Actually, the dervish and the ghost are pretty easy to deter since they're one-trick ponies...

 Now, since the BBEG knows the party, and is expecting them to show up at some point, he should be well-prepared for their standard operating procedures. Make sure the party faces him on his terms. He should have the homefield advantage and use it viciously. In fact, if the BBEG gets to pick the location of the final showdown, he should have it set up as a gauntlet just to get within striking distance.

 The dervish (never seen any of that "chozo" stuff before - what book is it from?) needs to move in order to get his extra attacks - if there's not enough room for him to move freely or he can't get to the bad guys, he's either much less effective or completely hosed depending on which methods you've used to pin him down. Make sure you're intimately familiar with the movement rules and all the little intricacies of the requirements for the character to pull off his tricks - in 3.5, there are usually a fair number of restrictions involved in when and how characters get to pull off their signature combos, especially if they're pretty complex and combine a lot of different elements.
Aside from using terrain such as small rooms, corridors, traps and tables/chairs/pillars to make navigating through the room harder, there are any number of spells and items (both magical and mundane) that can slow, entangle, or otherwise impede his progress. In fact, one of the wizard's underlings should be standing by with a readied action (trigger: when the character moves more than a certain distance) to hit them with a ranged weapon or other attack that can trip them. This should be used very strategically - pick the time when it will have the most effect both theatrically and tactically. Only ever do this twice in one fight though (at least to the same character) - the first time it will be irritating, the second time it will have the player out for the enemy's blood. Don't do it a third time (and never on consecutive rounds) because then you're reaching the point where the player will start to take it personally.
 There should also be hordes of minions for the guy to blow through - if he wants to hit something, give him something completely expendable to hit. You can bog him down with meatshields while still letting him ricochet around the battlefield slicing heads. If there's some sort of plot device actually producing these speedbumps, then that thing becomes an obstacle that the dervish presumably needs the help of the other party members to shut down, making it so that the party has to accomplish more than one goal to suceed.

 The ghost is even easier to stymy, even without giving the BBEG's underlings protection against possession - it's a hell of a lot easier for the wizard and the rest of team Bad Guy to just isolate/immobilize/kill their own people once the ghost has taken control of them than to actually kill the ghost itself. The ghost most likely has even more restrictions, limitations, and prerequisites for his possession trick than the dervish's twirling - at the very least, possession has a limited range.
The wizard should have a couple of temporary protections and ways to foil the ghost, but the ghost (with the help of the spellcasters) should be able to overcome them.

 The gadgeteer should be spending most of the fight pulling magic junk out of his pockets as fast as his action economy will allow - there should be any number of failsafes, contingencies, traps, buff spells and protections to overcome. Force him to choose every turn between buffing one of his allies and whittling away at the bad guys' defences and protections.

 For the spark-mage, throw in a handful of melee guys and a ranged guy or two that are resistant/immune to lightning - hell, have the bad guys trot out a flesh golem to chase the caster around, they're healed by lightning. Since there's at least a certain number of enemies that are guaranteed to survive the mage's initial assault, if not either be only slightly inconvenienced by it or actually helped, he'll need the rest of the party's help to keep them away from him long enough to find a non-lightning way to deal with them. If he walked into the fight with nothing but a straight lightning-damage blaster set-up for his memorized spells, the fight just got a lot tougher since he won't be as able to contribute to helping the other party members get past their own obstacles.
 If the BBEG has the ability to set up any sort of anti-magic fields, they should be placed tactically on the battlefield rather than having the BBEG stand in one defensively or try to cast it on the party's casters - if the BBEG is in some hard-to-reach place or in a well-defended position, then any anti-magic should be concentrated on those areas of the battlefield where it would be most advantageous for the party to cast from. Because of the nature of blasts and bursts and the fact that spells require line-of-effect (if not direct line-of-sight) to their targets, making sure that the blaster can't hit the whole battlefield and has to choose his positioning carefully to engage multiple targets can take a huge of chunk damage potential away from the blaster while still letting him rain hell down on his opponents. Alternately, the same pupose can also be served by the terrain-based obstacles you're using to slow down the dervish.