It's funny, but defending cartwheel passes is very rare in this position. In London or Williams guard, your opponent is positioned more with his lat against your mid thigh, and your angle isn't as extreme as this. In this guard, your opponent is wedged into your crotch, with your entire upper body as a post. It is VERY difficult to cartwheel here.
I find that preventing the roll is the only real battle. But a very winnable battle.