I use my OSS for shaping risers and profile sanding the back of the riser to match my form. My original was a piece odf 1/4" plywood with a hole in it, with a guide bearing at the hole that my template rubbed against. It works well, but saw a video on youtube that I thought might be a better system so put it into action. Had a couple drum sanding bits for my drill press that have a bearing on the bottom of them for pattern sanding which are just a fuzz over 2' diameter, and had the right size hole to fit the shaft on my OSS. Added a couple washers underneath for spacers.
I'll have to change my template to a thicker base, and a lil fine tuning yet, but this should do the job, as well as work better for other pattern sanding tasks. You could easily make the bearings out of plywood with a hole saw, or buy some nylon washers and stack to get to the thickness you need to work with the up and down action of the OSS.