So, I decided to go crazy with 608 sealed bearings- they are cheap, and I have a bunch left over from the original MendelMax build. I replaced the right-hand side guide post on the upper guide with a bearing, and created a new lower guide with two bearings.
|New upper filament guide|
|New lower filament guide|
I posted the files on Thingiverse: http://www.thingiverse.com/thing:199104