I just installed the M3 - SMG steering wheel with paddleshifts on my 540i. The procedure is exactly the same for the X5 and a couple of people have already done this mod. I believe there is a write-up under the articles section. If anyone wants to install the SMG wheel, I will be glad to help. It's not very difficult at all...

See this thread with pics...

http://www.xoutpost.com/x5-e53-forum/...ing-wheel.html