I don't use my filament run-out sensor, and it dangles off the side. To replace it, I made this filament roller guide. No need to reinvent the wheel, so I didn't. I am using the bearing spacer and wheel from this design.
https://www.thingiverse.com/thing:4590086
As agent9 suggests in his description, I am using a VXB 608ZZ Skateboard Bearing from Amazon along with an M3 screw and nut.
The author remixed this model.