...or a thicker head gasket. I don't know these are available for a Mercedes, but VW sells head gaskets in three thicknesses. IIRC, the difference between each one is about half a compression point.

Some of the TDI guys have been removing their glowplugs to reduce compression. This is fine on a TDI if the outdoor temperature is above 30 degrees, but it wouldn't work on a Mercedes.

Add an intercooler, and you will have room to tinker without having to reduce compression.