to change the dish you will need a new inner and outer... so all you're really keeping is the centre piece.
keeping in mind that would be changing the offset of the wheel alot... I was thiking about getting two of my 3-piece wheels made thinner as to clear the front suspension on my car... was going to cost about 350 each in sydney.. (can't remember how much exactly - but certainly wouldn't be cost effective for 4 for teh dishh).