Oh, my bad.
Edit:
After rereading the retraining rules I see the class levels can't be swapped out. You need rebuilding. And at least for your particular idea I really don't like how much DM fiat is required to accomplish that rebuilding since it calls for a quest. Too bad, too. After you mentioned it I thought of using the method for sheningans with the big guy is with me build+leadership to get cohorts at higher level than the original character in a chain until the highest level one can cast fusion+astral seed to turn them all (and their psicrystals) into a single character. Fix the class levels and construct hd as needed; but now that I reread that it's a lot harder to do.
Blegh...hate relying on DM fiat.