Well, the solution Wizards seems to have finally found by the end of 3.x was specific polymorphing spells - one lets you take troll form, one lets you take dragon, etc. I think it's a good solution, if not any easy one since you'd have to have one for each form. You could do the same thing with psionics - just take the specific-form spells and convert them, and it should work out okay. You don't even have to worry about augments.
Another psionics-specific idea I just had was a single polymorph/metamorphosis power that gives you specific bonuses or a specific form, but that you can augment to take different forms or get better bonuses. I don't play with psionics enough to be able to come up with specifics, but it's a workable idea, right?