It may keep it from ramming into you but wont do jack for lateral support whilst traversing a slope.
A better way--if there are two of you--is to be roped up and have a prussik running from the back of the sled to the rope. If you practice good rope management, i.e. keeping it fairly taught between the two of you, gravities pull on the downward side will be minimized. There's no way of completely eliminating it but this was the best we could do.
We tried the PVC pole attachment to the sled worked ok for keeping the sled fram knocking into you from behind but you still have to be careful that you dont get knocked off balance when the poles get slammed with all that weight.
Sleds suck.