Just get a bare stiff wire and feed it in to the rear and push it through. I used a ridiculously large paper clip that was coated in plastic. I removed the coating on the portion I inserted and straightened it out keeping a bend at the end coated in the plastic and pushed the filament through with steady pressure. I kept at it and during the process kept substituting the wire for a fresh filament making sure that I didn't insert the wire to far to damage anything. Worked like a charm and took five to ten minutes.
