I keep my filament rolls behind the printer on a separate stand and route the filament over the top of the prusa i3 frame and down into the top of the extruder. This guide clips to the top of the frame and keeps the filament from scraping on the frame, as well as cleaning dust off when the extruder pulls it through.
Prints without support. Cut a section of sponge, fold it around your filament then push into the rear of the guide. Clip the guide to the top of your prusa i3 aluminium frame.