because I don't want the entity to face into the direction of the bone. This function will, as far as I know, only correct the pan and the tilt angle, but the roll angle will be wrong then...

I need pan and tilt to face forward, and then need it to roll until its local z axis points along the normal of the attached surface.

Edit: if I make it point into the direction of the bone using ent_bonerotate, there's a (theoretically) infinite number of roll angles it could end up at, right?