The way I do cross wind take-off's in the 757 is to put up to 2 units of aileron in, due to spoiler drag. But then as rotation is called apply more into wind aileron as the aircraft is rotated. This means that the spoilers have not compromised your position on the runway for V1 or rotate, but you wont hit a pod during the actual rotation.
The change in Vmcg is not quantified, that I have seen, for the 757. So its best not to try and second guess it.
Of course I stand to get shot down in flames for all this!
