More labour intensive, but this will work too. Go to the Ruby section and download Didier's Divide script Draw your arc with the arc tool, and then divide it into the require number of segments. Didier's script will place construction points (cpoints) at the dividing points. You can also specify the number of segments making up the arc after selecting the tool and before drawing the arc (check out Help). Place a construction point at the insertion point for your column a then make the column and its cpoint a component. Use the move + copy option to snap your column to the cpoints on the arc. Delete the cpoints.