The scripting community at large has done a bang up job of trying to get around this problem, but we want official support on this. Allow a method for copying a prim or linked object, but have it mirrored on the plane that it's dragged onto. So if you have say, a left wing that curves forward and is properly rotated and everything, you can drag the local axis towards the left or right of the wing and get a properly mirrored right wing that curves the same way.
If it can be done on a prim by prim basis, it should be possible to do it on a multi-prim object basis.