This is an interesting feat which I have originally thought of performing myself at once. That said, you need to be a talented frontbender. I am not flexible enough right now, I know this. I would not call it impossible, just rare. There are 'selfsuck' males who are able to suck their own, so I don't see why they could not also suck something on top of it. That said... look at this theoretical act from a LADY's perspective... you're going to look really ridiculous doing it. Since sex is very mental for many women, this might be a turnoff. As a guy, I'm real fascinated iwth the idea, but from the pics I have looked up, the guys are real scrunched up while they hyperflex their spines, it just looks awkward and doglike. We don't look at ourselves while we beat off so it's fine for that, but unless a lady has her eyes closed, she's going to fet a big view of your spine joints jutting out of your back and it might be quite appalling.