basically you just need to solve for X, where X is the AP coefficient.
for example with heroic throw you would set up the equation like this:
Actual damage (on a boss dummy, no debuffs on it) = Various DIM's(damage increase modifiers) * (armor DIM) * X*AP
The Armor DIM is (26070/(26070+11977)), and as far as I am aware there aren't any DIM's that modify heroic throw's damage
if you get a really strange x value, then that probably means that there is a +n damage in there, or you made a mistake with your math