Mix a little epoxy, and add about twice or three times that volume of silica. Add sanding dust until the color matches (it won't change much during cure). It may be a bit grainier than you like, so here's a tip. Tool the joint with a dowel. When cured, wrap sandpaper around the same dowel and sand away. If you use a 1/4" dowel or the bead edge of a scrap strip, you have a ready supply of sanding blocks with the proper radius. Glue or staple the paper to the strip and you're good to go.