Have seen a few guys do it, not sure what they used but I would think you need something durable like powder coat. It looks pretty good I'll try to find a few pictures of a couple I have seen.
A quick look all I could find was a photoshop.... Second picture down in this thread.
http://www.xbimmers.com/forums/showthread.php?t=723196
Here is one that is real.
http://www.xbimmers.com/forums/showt...&highlight=Bbs
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X5M, Eisenmann exhaust, 22" HRE wheels, catless down pipes, Stage II tune/X5 Diesel, Lowered & Tuned