Until an alternative or additional mechanic might be integrated into the Echo system sometime in the future, it would be best that Ben's Echoes would unlock and focus on building up select transformations at a time. Of course, Tier 2 Echoes would speed that along by granting multiple abilities at a time or unlocking a transformation with the most basic powers it's got - additionally, in certain cases it may not be infeasible to bundle up powers and/or knowledge of how to use powers that may be thought of as extensions or alternative uses of one that the form already has for gain through a Tier 2.