This is a Bowden Tube Guide I originally made for the Space Pi filament dryer, but it can be used elsewhere as well.
It can also be scaled up to fit thicker filaments, as the model is made for 1.75mm filaments.

To use it, insert the tube inside the wider section, and use a hair dryer to shape it to the natural curve you want (print with PLA to make this easy, you might need a heat gun if you use a different plastic).

Included in the ZIP file is the FreeCAD file, so you can alter it to your needs.