Having been bitten by some clogging recently I decided to design a filament cleaner that fitted nicely on the extruder of my Mini. There are two pockets for the idler bolt nuts that I used to mount the cleaner on the extruder body. I added a drip of (IKEA) mineral oil to make sure all dust stays in the sponge.

update: I shaved a bit off of the studs to make them fit slightly better. I think you still need to file them down until they fit snugly though.