They cannot make room for this necessarily memory without giving up some of the great features this game has to offer.
They will not give all that up just so you can play with female characters, live with it. They cannot release it as a DLC either because new character models require RAM (random access memory), which has nothing to do with how much the disk can hold.
This only applies to the consoles (PS3/360). I guess it's technically possible on the PC version.