Hold on a second, grappler. This is for the big kids only - the kids who know their way around the pool and can swim in the deep end without any floaty things. If you're still playing in the shallow end and need mom's supervision, that's OK - you can watch and take it in for future reference.
Damn, I just love this technique. We've been playing around with this hook from spiderguard at my academy for many years now. I typically grip on the same side as the hook myself, but GB Escondido coach and Carlos Gracie Jr. black belt, Magid Hage is using a cross-grip (Braulio Estima style). Inverting yourself and catching the omoplat off the shoulder roll is tricky, but it works and can be very effective. And, as long as you maintain the hook, you should remain safe and be able to recapture guard if the submission fall apart.
Oh, and I was only half joking about this being for the advanced kids only. Anyone can try it. You're just much more likely to fail miserably with it if unless you gots some skills. Go for it.