I actually think I got it, but not confident it is the best solution.

vec_set(my.x, my.skill1);
vec_rotate(my.x, arcade_Case.pan);
vec_add(my.x, arcade_Case.x);
vec_set(my.pan, arcade_Case.pan);
ang_rotate(my.pan, vector(my.StartPanOffset, my.StartTiltOffset, my.StartRollOffset));