once they have the two hands in, you can reduce the effectiveness of their choke by putting your head onto their chest. You have to keep your ear glued to them, and it becomes difficult to finish (difficult, not impossible). This can buy you some time to escape or break. This works best when you are on top, almost useless from the bottom of a knee-ride. I've used this on people who bait a guard pass hoping that they will be able to baseball bat choke me. Go for the pass really slowly so that I can control where my body and theirs end up, and then smash my ear into their chest and hold on with both arms. Don't let them have a single inch of separation with which to apply the choke.
prevention is much better though.