http://episteme.arstechnica.com/eve/...m/972005566831
Oops...if you could return either one, I would go that route and either find a video card that will fit that you like or a different motherboard that has what you need, except for the infringing southbridge heatsink.
I always recommend not to "void the warranty" by altering or modding an expensive piece of hardware. I see hardware everyday that fails in a short time, and it sucks to be out the money if they inspect the card and find anything wrong.
You can always get the HR-03 (the only one I know of for replacement), and just keep your stock heatsink and replace it on the card if it goes bad. Then send it back for warranty replacement. As long as you don't damage the sink when you take it off, they may not be able to tell you removed it (hopefully).