RE: Warped ARF Stab- How to fix it?
If the stab were twisted, you would have to fix it. But why do you feel that a bowed stab is a problem? As I recall the 4 star has separate elevators, so you don't have to worry about a one piece elevator not fitting the warp. 3/16" of total dihedral (or anhedral) in the stab will have no effect on the way it flies. A number of full scales have dihedral in the stab and a few have anhedral. Old style pattern models often had anhedral, and a whole lot more than 3/16".
If heli's trick doesn't work, use it as is.
Jim