MS4 - How to add a custom .drm file to appear as a instrument.

I have a custom .drm file for a unique drum instrument. How do I get my .drm file to show up anywhere? I'd like to make a template for it, but it's not a selectable instrument.

History:
In MS3 I accomplished this by making my own instruments.xml file and linking to it. It had all of the instruments I created all mapped to a custom soundfount. In MS4, anything added to the instruments.xml file is ignored and custom instruments.xml extensions are not supported. I understand I should be able to recreate the same functionality in MS4 using a custom .drm file and templates, but I'm struggling to figure out how to make the instruments appear so they can be made part of the template. I feel like I may be missing something simple, but after several hours poking at this I have not made any progress.
Thanks for any help.