I thought I replied this yesterday, but it musn't have uploaded.
Anyway, if you make sure the 'stud' skin of your composite has the same fill as you stud walls, then it should be quite easy. You just need to intersect the composite wall with the angled stud wall (Tools>Line Extras>Intersect) then select your two stud walls and intersect them in the same manner. Whooshka!
It is all about the order!
Cheers,
Link.