I wanted a reverse bowden system for my enclosure as I now mount the spool holder on the side.
Works as well for the other use cases you will find when you are looking for such a system for your printer.
The main reason I designed this was, that I was unhappy with the solutions I found and wanted something clean, fixed in place and sturdy, not some attachment.
This design replaces the original "filament-sensor-cover.stl" by Prusa which can be found on github.
The most important part is that you need a bowden tube coupler, which passes the tube through. (see pictures and parts section)
My coupler was M10, and must be screwed in with the help of a wrench.
I recommend printing this in Black and PETG, though PLA should work too.
edit after comment:
This bowden connecter should be what you need. I has the wide opening below, so that the tube can be passed through.
This was made from scratch in OnShape, here are the source files.