In this video I show an option for when your opponent is keeping his head low in Kesa Gatame. This move does not require as much flexibility as you think and can work well for you even if your opponent has their head very low (although if his head is touching your shoulder or laying directly on your face it may be difficult).
Make sure to cup behind your knee and leave as deep a pocket in your hand as you can. The deeper the pocket the better grip on his/her chin you will have. Once you swing that leg around the face and the hand catches it should be fairly easy to push them away with your leg.
You can typically get one good attempt at this against an opponent who sits low but does not bury the head. If you try it and fail be prepared for your opponent to make life very uncomfortable and up the domination of this position.