I did this years ago, the best thing to do is, cut the LED wire, then cut and run the wire that goes to the running/signal light for the headlight and run it to a resistor to take the load (25watt load.) After that you tap into the fender side signal wire and run the wire back to the headlights running/signal light wire. No errors, and will signal correctly.
Here is my old thread, works for all E92/E93s, and all E90/E92/E93 M3s...
http://www.e90post.com/forums/showthread.php?t=64702