I build a Mural whiteboard plotter (https://getmural.me/), which is intended to have the belts hanging off of thumb tacks. I wanted to use it on a white board so I designed a mount that would sit on the corners of the white board. The belt mount is mirrored on the part so you can print two copies of the part and not be annoyed by having mirror imaged ones and figuring out which one goes on which side.

(Side note: the Mural plotter is great and I would recommend checking it out if you're interested in a low cost plotter.)

Printed in PLA at 0.2mm layer height. FreeCAD files are included if you need to adjust the tolerances. I didn't make it parametric, so good good luck with that. I apologize for nothing.