I dont know, but I happen to know for a fact that kotegaishi works just fine when someone has the mount on you.
I'd have to see it to believe it. The way I ride mount is usually in one of two forms
1) grapevined legs, arms out wide for base, digging my weight right into your sternum keeping you from breathing and waiting for the submission.
2) Riding up very high with my legs pushing your arms up over your head, punching you in the face or preparing an armbar with a 2 on 1 grip.
In the mount you have no leverage, no strength, and no way of moving yourself to an angle on me. Essentially it should be impossible to apply any significant turn to my wrist. The person in the mount has the ability to use leverage, strength, weight, and his free hand to pound on you as needed. I'd probably be willing to give my hand to a person while I'm in the mount if it keeps them busy while I start dropping elbows.