Filament Guide for DaVinci

I've been feeding filament from an external spool on my DaVinci 1.0 using my Big Spool Holder (http://www.thingiverse.com/thing:583800), which was derived from Ranh316's DaVinci Rear Filament Spool Hanger (http://www.thingiverse.com/thing:409100).
Works OK but I don't like the built in filament guide: It crimps the filament if you open the top too far and makes changing filament tricky. I tried passing the filament directly through the rear slot, but it tends to pull the filament off the si