By inserting a 10-28 set screw in this hole in the drive plate...
 

...and tightening it down with a 3/32" Allen wrench...
 

...until it is flush with the top of the plate, you can rig a temporary fix for the problem.
 

In normal use, the screw will protrude from the bottom of the drive plate.  This is OK in most situations.  The screw shouldn't touch anything as it spins around.
 

When it comes time to use your invention, just remove the normal drive pin and use your Allen wrench to loosen the set screw...
 

...until it protrudes far enough to use as a drive pin for your split reels.
 

Use a piece of Gaffer's Tape to store the wrench in a convenient place until you need it.