I dont know of a way to do what you are asking. In order to get the opp hand, you have to derive the part, then mirror it. Even if you do the copy design on the idw and manually derive/mirror the parts. Then use the replace model reference command on the idw to get in the derived/mirrored part. Even after all that work, you will lose all the dims on the idw.
we had a huge job a couple yrs ago that had a right/left hand assembly. we got all the idws complete then wanted to do a mirror on the iam and the idws. We ended up saving the idws all in autocad, then mirroring it there..... what a mess. We spent more time getting that straightend out than we would have if we had went ahead and modeled it correctly in Inventor. Since we did part of it in inventor and part in acad, we couldn't get a complete BOM.
Another problem was that we couldnt just blindly mirror the entire assembly. Some of the parts were truely mirrors but other were not mirror images, they could just be simply flipped over. they were the same parts. not sure if this is your situation or not...just what I ran into.