I could do this when I was much younger, but probably not anymore. I also used to be able to put my foot behind my head. I've got some back problems these days, so I don't try that anymore. I agree with gloryholeprincess. Try yoga. But don't be expecting to suck your dick next week. If there were a quick way to become flexible enough to self-suck, very few men would ever leave their homes.
I've seen a video of a guy sucking his own dick along with a girl. It was posted on xtube, but doesn't seem to be there anymore. It was pretty fucking hot.