Just spotted this so apologies for being late to the party.If its anything like a W204, the rear brake pipes can be replaced without dropping the sub frame.
Had mine done for a princely £160. Not at a MB specialist garage though.
It may be useful to know (although perhaps not in this instance) that the subframe needs to be dropped in order to replace the rear brake pipes on a PFL W212. Had to have mine done a few weeks ago to pass the MoT.