Curiosity...
I know that I can do this, I did it once before several years ago. Problem is, I have absolutely no idea how I managed it, especially as I don't remember being particularly turned on at the time.
There are several tips online as to how it might be achieved, but one site had a tip I'd never seen before. Ben Wa balls. I checked them out and found a site that had really reasonable prices, so I've ordered some (see who's the first to correctly guess which colour!).
I'm hoping that they'll help me in my quest for the ultimate orgasm, though even if they don't I'm sure that they'll benefit me in other ways (not to mention my OH!).