Well, swallowing whole wouldn't necessarily be quite as powerful as it is for other creatures. For one thing, they would have no natural damage in their stomach. They'd have to put features in it (which means loosing features on the outside). Also they'd then have to use those features (though I may do something like allowing a single standard action in the stomach each round allowing for 1 attack, with full attacks or the like requiring giving up actions outside). Also as you can't see in your stomach, they'd have concealment unless you put an eye in there. Then there is the fact they get to do easy damage to you (can't dodge), and are safe from you allies (unless you swallow them too), and can cut a hole to get out of you.
Edit: also changed health gained to full charisma mod, and left it at 2 rounds later.
Owrtho