At Velocity we used a mixer gadget.  Both cables from the panel come together side by side.  A third cable attaches from the opposite direction.  The three are secured with a bolt.  
The down-side is that the co-pilot control doubles the friction, makes either control harder to manipulate,  And if either control has the friction lock set, the other control cannot move either.
Consider the hazards before going that way.  
Rick Hole