I added the Prusa i3 Mk3 Z-Tops with Reverse Bowden Mount Option by ctilley to my Prusa i3 Mk 3, and it works great, but I found it inconvenient to use with the Original Prusa i3 MK3 ENCLOSURE - Ikea Lack table, since there's not much room inside the enclosure for a filament spool. This thing allows the filament spool to be placed on top of the enclosure, optionally inside a dry box.
To install the thing, drill a pilot hole through the top of the Lack table, near the center of the front edge. Then use a 1/2 inch spade bit to drill a hole through the top surface of the table top, and a 5/8 inch spade bit to drill a hole through the bottom surface of the table top. Insert the spool side part into the upper hole, and the extruder side part through the lower hole, and thread the two parts together. Thread a PC4-M6 pneumatic straight fitting into each of the two parts. A 20 inch length of 2 mm ID PTFE Teflon tube (the reverse Bowden tube) connects the lower pneumatic straight fitting to the pneumatic straight fitting on the extruder cover. (I replaced the extruder cover on my Prusa i3 MK3 with the Prusa mk3 filament sensor cover with m6 threads for reverse bowden). Finally, put a short length of PTFE tube in the upper pneumatic straight fitting if feeding filament directly from a spool, or alternatively connect the PTFE tube from a drybox.
I made this thing in a variety of materials: Hatchbox PLA (yellow), eSUN ABS+ (black), and Quantum 3D ABS Plus (yellow). The choice of material is not critical.