I did not have enough room to fit the MMU3 buffer beside my MK3S so I made a custom size Skadis to fit the MMU3 on the wall. It is very sturdy when it is in place. You need some M3 nuts en screws to fit the base and top to the new plateholder. 

All printed flat with no supports needed, I used 4 walls with 20% infill. Notice that the parts that go into the Skadis holes have extra infill in the design.