I remember watching the cartoon Jumanji when I was a kid and one episode had Allen getting sent to this nightmare world. At one point, he's in this field of giant flowers and one latches onto his face and inflates him.
I think things like that should start making their way into inflation stories. Plants that inflate people by latching onto them or with their pollen, animals and insects with with bites or something that inflate people. You know, just add some spice into the inflation process. Helium tanks and air pumps are good, but they just get boring after awhile. I think some freaky inflation stuff like this would make some great stories.
Those things have been done to varying degrees of success. Sixstar's one series of stories is based on genetically altered bees though I can't remember the name of the story. But you're right, it isn't done nearly as often and would make for some interesting imagery.
http://harrisonford08.deviantart.com/ http://groups.yahoo.com/group/ijartist/