Here's an idea. Attach the aft end of the middle rudder pedal slider to the forward end of the aft rudder pedal slider with an easily removable cable.

When you're alone in the middle, the middle pedals would pull on the aft pedal sliders and move the rudder.

When you're not alone, unhook the cables to the middle cockpit and stow them away. You would also have to figure out how to make the middle rudder pedals lock in place when there is someone in the middle. Perhaps by using a locking pin of some sort.