Dan's right. You could use a piece of dowel that matches your grooves and wrap it with sandpaper.
Another option would be to cut a strip of sandpaper slightly narrower than your groove, cut a slit with the band saw in the end of a 1/2" (or?) dowel. make the cut slightly longer than the width of your sandpaper strip and insert the strip into the saw cut deep enough so that you can use a rubber band on the slit to tighten the grip on the paper. Then chuck it in a drill.
'The true soldier fights not because he hates what is in front of him, but because he loves what is behind him.' G. K. Chesterton
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