I recently needed an alternate filament guide for the Opiliones, for use with the extra filament holder I recently put together. So, I came up with this design...
It seems to work just fine, but please keep in mind that it's a first iteration & things may need some tweaking.
[Edit: Had missed to add the STEP files... If it needs tweaking, you'll be needing those. :-) ]
You'll want to make sure to use screws with low heads: these should NOT protrude from the end caps. Should the guide ever fall down, any protruded screw heads might damage the glass bed.