Hi there, good on you to find this work-around. Nevertheless, MDG-M shouldn't ignore MARC assignments... Are you a recent SP level for MDG6.1?
MARD was indeed only added with MDG7. You could extend the data model with an entity and the UI with a MARD table easily (check guides in http://scn.sap.com/docs/DOC-7858#section2). Adding the storage location to the initial screen is (to the best of my knowledge) possible but harder.
The recommended approach is to upgrade to MDG7 (which is Generally Available).
Regards, Ingo