Unless I'm missing something, this should be as simple as taking the current aim (vector from enemy to player in the enemy's local space) and adding the player's velocity vector. When I sketched it out quick it seemed to me that I was literally just drawing the old 'tip-to-tail' vector addition method, so it should work out just fine.
As long as you use the resulting vector as the projectile's velocity, it should be directly on course to hit the player (assuming I didn't mess up and they maintain their course).
All in all, should be something like this (pseudocode)
aimVector = (x,y) - (ex, ey)
aimVector += (vx, vy)