What leads you to that conclusion? The last time I looked reservists were being enrolled in the primary reserve not the Baker Street Rifles. One can't be transferred a reservist to the regular force "component" without consent but to another unit . . . it could happen. Then again they could just stop showing up or taking a release like they do now . . . so why do it?
The issue with combat service support trades is a tough one because of the career profile and promotion opportunities is limited by the army reserve establishment. For the ARE the career chain stops at MCpl for the old RMS trade within any given unit, albeit the unit can rig the system up to WO if one misuses the Trg WO ATR position. And, of course there's that old - put them on Class B to take the place of that RegF Sgt that doesn't get posted in any more.
It's a very challenging problem seeing as there are both situations where you have multiple units in a tight urban area and ones where you dispersed units and subunits and an administrative system that is not online friendly and needs lots of short, face-to-face interactions.
IMHO, the only real working solution is to have a much more computer-friendly admin system but with any job that needs full-time attention, which admin does, handled by full-timers. I think it's not hard to train on a part-time basis, but it's hard to administer a unit that way. I think admin needs running like a help desk where you have one easily trackable "user file" with full-timers working both at units and at online/phone line regional help desks. First though, one needs to simplify admin and finance.
Tough problem.