Locking key for Ultimaker filament feeder (aka "extruder")

Tired of the feeder that wants to detach itself from the ultimaker frame each time you push the filament upwards manually?

Scared that it falls off each time you move your box around?

Just stick this thing in the free space above the extruder arms to lock it in place.

OK the best surely would be not to have to push the filament by hand at all, but at least now I do not need both hands to do so :)