The best way I have found to deal with these "unorthodox" shapes is to revert to the underlying geometry. We often overlook the fact that Solidworks can very easily mate to planes, sketch entities (lines, arcs, points), axes (both temporary and basic), etc.
Frankly, I am amazed at how easily Solidworks can handle some of the more complex shapes. When I think of the extreme mathematical gymnastics involved in the underlying code my mind starts to swim and I become faint ...