UPDATE:
This retrofit is possible, and came out great. This means you can use the stock F8X or Autotechnic paddles with this retrofit.
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Stumbled across this DIY to fit F8X M DCT Paddles onto non M cars and I realized how similar the F20 paddles are to the E82 paddles. Possibly we could retrofit as well using option 2 (removing the paddles from the housing)
http://babybmw.net/forum/viewtopic.php?f=63&t=83600
I believe this could be possible on the 135i DCT by looking at our stock DCT paddles and the F20 Auto paddles. Only visual difference is the rubber boot.
Thought this was a good option to look into since we never could figure out how to get the E9X M DCT paddles to work on the E82. I will keep an eye out on eBay for a cheap set to look into this more.
E82:
F20:
F8X: