Basically the idea is to use weights (80 grams seems about right) to pull the slack out of the filament after ejecting. In order to route the tubes out of the front of the enclosure, I mounted the MMU backwards. Might prevent printing tall objects, but for what I print I don't care.

The tube router piece is screwed onto the front of the enclosure with M3 screws / nuts.

The filament hooks are designed to not get caught on other things.

Who knows if this will work long term - but it's been good for about 100 changes so far with no issues.

Filling the weight pieces with cement or something heavy. 

In action