Women tend to have much more flexibility in their shoulders, which is why this is an especially good technique for them.
I have started using a reverse grip, ie gable grip, with this choke, and find it gives you a lot more flexibility to get your shoulder high.
I remember in swim team too, women could swim butterfly easier than men because their shoulders are so much more flexible, it's easier for them to clear their arms. For men to swim butterfly, you have to really swim hard to get that clearance.
I dont think it requires special shoulder flexibility. I've done it before while rolling and my shoulders are not very flexible at all. You just really need to get a deep hold on their neck before connecting your hands and throwing that forarm up over the guys shoulder, you can see how high my team mate gets it and hes average in terms of flexibility.