Without knowing the exact expression in question, it's hard to say for sure. But you could, I suppose, so something like the following:

. . . . .cos(s)cos(t) – Asin(s)sin(t) = [cos(s)cos(t) - sin(s)sin(t)] - (A - 1)sin(s)sin(t)

I don't know if that will help at all, though....