Getting the Two-Headed or more, requires an extra 2hd per head.
The basic 2Headed is 2 racial hd + the 2 LA ... kinda sucks, possibly useful.
Assuming la buy-off is in the cards, it's just a 2 "level" hit.
edit ... hmm ... how about going Persisted Polymorph and Hydra something?
Multivoice wouldn't work after a dispel, but reload-able.