Custom configuration variable creation

I am attempting to create custom configuration variables in order for the workset configuration file to find a directory path defined by the variables (similar to defining MS_DEF to point to a particular directory for finding dgn files). In particular, I am attempting to have two custom variables (MS_POINTCLOUDDIR and MS_REALITYMESHDIR) located within the workset.cfg file point to directories when one executes Point Cloud> Attach and Reality Mesh> Attach. Any idea how I may get this concept to work? Am I merely missing configuration variables which already exist (as they exist for attaching dgns, refs, and images)?

Thanks!

Mark