The invoker spell "wall of hestavar" creates an unbreakable solid barrier, but it is also a sustain minor. This could be used by an ally to keep you inside, or used by you once inside to block the door.

The wizard spell "wall of ice" would also be affective, because you could stack the blocks so that he has to break through 3 layers before reaching the door. Thats 150 damage he has to deal, and he takes 2d6 damage each time he hits a block, AND 2d6+int when starts his turn next to it. Depending on how much damage he does , thats at least 100 damage before he breaks out.

The wizard spell "wall of force" could also be used. It takes 200 damage before falling, and can be attacked through if you are ranged or have reach. Teleporters can get through it though.

By RAW if you teleport a huge or gargantuan creature into the space, they will not be able to exit the room, even if they are squeezing. This could prove a useful tactic against huge monsters if your party has alot of damageing zone. The melee character attacks from the doorway, and the monster is forced to stay inside X number of zones until it dies.

You could use one or more immovable shafts placed in the doorway to restrict his ability to escape even if the door is open. Assuming the monster automatically suceeds on the strength check, it is still a minor action to place a shaft, and a standard action to move it. You can place one on turn 2, if you have it ready in your hand. Turn 3 you can place another one, minor to retrive, minor to place. Continue adding one every turn if you want. If you have quickdraw, you can place 2 each turn. Obviously because of cost, this would only be possible at a higher level. If you can a ring of free time, and quickdraw you could place 3 shafts each turn, and still be able to standard attack. This is probably overkill, but any character could do it, and it would look hilarious.

A wonderous item "phantom soldier" could be used to block the inner or outer square. Although RAW does not say if it is solid or phasing. Just that it is an "illusion"

A ring of personal gravity could be activated so that you and him are stuck in melee inside the room. Unless he has teleport, or can somehow push/pull/slide himself.

For maximum retardation, use this against a foe who is unable to breath underwater.
Use a scroll of waterbreathing on yourself before the start of the encounter.
Be using 4 ring's of free time. 1 on each hand, one many fingered gloves, 1 mumified hand.
Multiclass druid to get wall of stone.
Be carrying 160(minimum 124) handy havarsacks, each fill with 1000lbs of water.
Have quickdraw.
Have a way to gain phasing.
Have a way to fly.
On turn 2, use a minor action to close the door, use whatever action to activate phasing, and a standard action to cast wall of stone, filling up most of the room, move up 3 squares to the corner above your enemy.
For the next 16-18 turns, spend all 7 minor acions opening haversacks, and emptying water into the room.
Laugh as your sworn enemy drowns to death.
Laugh harder 5 minutes later, at your teams confusion when a torrent of gravel and water pour out of the once empty room.