If you use one setup the majority of the time, perhaps it's worth considering buying a second car? This is first of all a good set of spares in meetings, and you can set up the second car in the different configuration - with a fitting setup to the shocks. I don't know how different the setups need to be on the 22 between rear and mid, but I can imagine that just swapping the gearbox isn't all you need to change on the car.
In the scenario I just described, a second hand car might do fine as a second car - but of course that all depends on your budget and how often you plan to switch between rear and mid
