You are right, his level 50 skill Ray Gun can only be learned by Mite, not by his future forms. So its unfortunate everyone's forced to evolve their Mite after the trials. Though, it isn't too long from that point when you can catch other Mites.
You can feed it a gem containing that move. I haven't checked all the moves, but most of them have gems so a familiar that you level before a move, or a move it would never learn anyways, can learn it.
Mind, the gems are of specific categories (fire, light, shadow, etc) and can only be fed to a compatible familiar. Ray Gun is a light gem iirc, and Mite's later forms can accept fire and light gems.
Alice returns in 2011, I'll be ready... http://www.ea.com/alice Inception ending spoiler: http://twitpic.com/26k9ub