I use the Ultimaker 2 Filament Guide (With bearing) from dirkdirk (http://www.thingiverse.com/thing:388560) on my Ultimaker. Based on it, I created a second filament guide that uses the same ball bearing and the wheel part from dirkdirk and can be mounted below the feeder.

To mount it, just unscrew the screw that holds the left motor cover and replace it with a ISO 7380 M3x20 that hold the filament guide and the motor cover.