Burger (BMS) makes one for the N55/54 that seems to work well.
Current: 2014 F15 xDrive35i | SG | XLine
Sold: 2013 E92 M3 | SG |ZCP | 6MT | M PE | M CFRS
Sold: 2011 F25 X3 xDrive35i | BS | M Sport
Sold: 2011 335i Performance Edition | BS | RWD | 6MT
Sold: 2009 X3 3.0si | AW