One popular method of increasing performance on Supercharged cars is using a smaller pulley. The smaller gearing increases the boost provided by the supercharger. I remember my Dad changing out a SC pulley on a 4.0 or 4.2 SC Jaguar Engine.
Nearly every aftermarket tuner offers smaller pulleys. UPD suggests via its product pages that 80mm is safe without a tune and 77mm will require a tune on the 2003-2007 M113K. Please note the picture used in this post is of the UPD page. Please consider using their stuff which is of high quality.
VRP has made its name tuning on the m113k platform and they too have quality pulleys with more focus on price. TunedMercedes is an authorized VRP dealer.