So, I'm a big fan of inflation stories (mostly inflation->floating) and from what I've seen, there are 6 main types of inflation stories. Here they are, in no particular order. Maybe this will spark someone to write their own inflation story, as I think there needs to be more out there . . . MORE I say!
1)Not inflation: The "Most realistic" of the stories, the person does NOT actually inflate, but instead they are in a suit or, sometimes, inflatable implants.
2)Altered Physics: The physics of the world simply allow for inflation. Just stick a helium hose in someone's mouth (or somewhere else) and turn on the gas. A variation on this is one species or mutant trait that allows inflation.
3)Super/Mad Science: Aliens, ray guns, super bloatation serums . . . all fall into this category. If they try to explain it with science, it falls into this area.
4)Magic: Ancient temples, magic spells, devices, strange old men on the subway offering "something special," abraca-Ohmygodyourfloating!
5)Psychic: The most under-written category I believe, I've only ever seen one psychic inflation story but it was well written. Never the less, they exist.
6)Unexplained: My least favorite category, this just has some woman start filling up for no rhyme or reason.
If someone can think of another, please tell me, but (as I see it) these are the six major options. Hopefully, by laying these out, I might have inspired someone. Now, if only I could finish my own story.
Which was the pyschic inflation story... I've been thinking of something like this... where the inflatee gets full control over the inflator's every move.
I'm trying to think of other methods but I think you may have it all covered. I mean Altered Physics covers the majority and anything else must depend on something that might just be within the realms of possibility (sci-fi), or something that defies explaination (magic, psychic) if you don't go with these then you pretty much have to leave it unexplained.
Personally... I prefer Altered Physics, I think that most of my stories involve it. I just like the manual world of pumps and hoses and all that. I know what pumping up an air bed feels like so it's easy to transfer that across to pumping up a girl.
Which one is the story you're doing?