I've given my PC's an 'ancient draconic' scroll that describes their destinies. The players have noticed one tiny (and very deliberate) mistake. The prophesy only mentions 9 of them. There are 11 PC's.
My players have taken this to mean that I plan to kill off 2 of them based on the discussions I overheard. Though it COULD just mean that 2 of them are not the 'real heroes' or that the prophesy is complete bunk or any number of other things.
This heroic destiny item seems to have worked somewhat better than I thought. It has gotten the players into the heroic mindset and has them actively looking for the designated tasks. The PC's have also learned that the last 20 sets of heroes died without completing any of them.