This guide can be installed without taking apart the frame. It is installed by the 4mm twist lock style frame nuts. If you do not have any, I am putting in the link to print your own, like I did. It bolts on the back side of the upper frame and is thin enough that it does not interfere with full Z axis travel. I have three guide end patterns. Solid where you thread the filament through the hole first. Slotted where you can slide the filament in the guide anytime (filament did flip out on me once). Rear slotted where it can be inserted near the spacer bar (untested at this time). Parts were made with generic PLA, 20% infill, 3 layer. Pads were incorporated on the long bar to help keep it down while printing to be cut away. Screws, I used two 4mm x 10 to bolt the short and long bar together, leave free enough for pivot and long bar to spacer, tighten. Two 4mm x 8 to bolt short bar to printer frame. One 4mm x 6 for guide end to spacer, leave loose to pivot. 

This is the site I used for the T-Nuts: Thing files for M3, M4 drop in T-nuts by swesen - Thingiverse . Print these 100% infill with brim.  After brim is cut off sand bottom until they freely rotate in slot. Preassemble short bar with two 4mm x 8 screws and T-nuts and tighten screws while holding bar all the way at the top of frame.