The tray part that I used was $14 on amazon - "Funtasica 7118064 /Centre Armrest Storage Insert Tray /51167118064", which doesn't seem to be available anymore, but there were other after market options for about the same price. Also, my 2012 335xi was a bit different - it had an additional cable that ran toward the back. So instead of trying to trace that down, I disassembled the part holding the electronics, then used an exacto knife to cut through the rubber piece that was holding all the cables together. Thus I could separate out that antenna-like cable and just leave it in place under the tray.
