I do what Dave M said, use a pin. Once to sand a number of constant camber curves I used multiple pins. 4 pins set in the line of the arc - 1 way to the left, inconjunction with the left center guide of the OSS as "infeed" guides, the center 2 were the "across the middle guide" and the rightmost of the four (with the right center guide) outfeed guides.
Scot