Wow, many lovely stories and ideas on this subject.
One of my fantasies is about injections into my outer labia. I read about it and have thought about it ever since, but I don't know if it's really possible to perform. In the story I read, saline solution was injected into the labia to make it swell.
I like to imagine this happening and of course I'd be strapped down to a gyn chair, my breast bound and swelling, my belly swelling from a huge enema...and then the sublime pain from the injections and my Dom fucking me.