The Prusa MMU buffer has never really struck me as being very practical. So I decided to design my own. After several iterations I came up with the mini buffer. Just connect it to the end of your MMU PTFE tube (using a bowden connector) and the filament just unspools into a loop. When the filament is required again it simple spools back in. No need for auto rewinding spool holders etc.
Optionally you can use 2 lengths of PTFE tubing if you feel that the filament is not feeding correctly without it.
You'll need a bowden connector and a 608 bearing which goes between the two halves of the wheel.
This shouldn't need supports, rafts etc.