I once had an RP in which the inflatee (*cough* me *cough*) gained a lot of weight before swelling up into a blueberry, though the weight gain continued alongside the inflation. It was interesting, and I wouldn't mind playing something like that again if I were in the mood for it.
Mixed expansion stories
I've always had fantasies involving mixed expansion where the inflatee begins with a sort of spontaneous weightgain/stuffing (of the non-blubber type,) reaches a large size and decides that's not big enough. From there on, they try to expand via air or other methods to get large enough.
The inflatees in this sort of expansion are egocentric and obsessed with getting as large as possible of course. So, the whole "not big enough" expansion scenario via weightgain then air works well.
Anyone else interested in this sort of expansion? I'm considering writing a couple of short stories based on it and just wanted to gauge interest.
A few mixed inflations I can recall:
Courtney's Tale has something like this. Courtney starts off thin, gains a lot of weight, and then has her husband inflate her with a bicycle pump.
Galaxy U features an alien who stores water in her breasts, which her body converts into hydrogen and oxygen.
Tales from the Bra 2, to Air is Human has a scene where a woman stuffs herself with candy, passes out, and then gets filled with water while she's unconscious.
As i imagine it, in order to inflate - in imaginary world of course - you first need to stuff yourself extremely. To the extent when in real world you would receive an injury. And then the body protects itself, so it temporarily turns a part of itself into gas, to avoid damage.
So for me there's no difference between stuffing and inflation - the former is the cause of the latter.
What to use for stuffing - sandwiches, water or helium - doesn't matter. Gases are just easier to use.
Also, it's possible to abuse this ability - say, trick body defences into believing it's in danger and must inflate. That's how inflation pills are working.
I like to imagine it all natural, no magic or hi-tech. Just a side effect - like getting tanned - which can be misused.
Sorry, said already too much ^_^
That is, in fact, an interesting topic, and one that doesn't get a whole lot of play. The only examples of "mixed" inflation stories I can readily think of off the top of my head are:
Essence of Justice - starts with water, ends with air
Another Nasty Sting - starts with water, ends with ice (because water expands as it freezes)
However, neither of these involved WG, and both were nonconsensual so they don't quite fit your mold of the inflatee *wanting* to grow larger by other means.
I'd be interested to see what you come up with.
Stories I have written