If this is really true (and I fully believe that it is), why not just interview individuals like a job interview rather than have them pitch ideas?
If you know the resulting product is almost certainly not going to look anything like what they're proposing, I would just try to swing some on-campus interviews at Stanford and UC Berkeley, hire the kids based on smarts & personality and then put them in a room and only then start talking about ideas.
Why bother reviewing their initial ideas at all (other than as an indicator of the aforementioned smarts & personality)?