I've built a quad recumbent. (https://quadrecumbent.blogspot.com) I'm looking for a way to control both rear deraileurs from one shifter. I've kicked around a couple of ideas like a slide control with the cables connected to it or a cam type device. I'm currently using the shift control for the left side from the right hand on the left bike. The problem is the shifting pattern is backwards and its difficult to remember some times that the left side goes the opposite way. Any ideas are extremely helpful.

Lets see if I can explain this...use one wire and run it from deraileur #1 through some housing to a cable stop. Now make a loop and run the wire through another stop and some housing back to deraileur #2. Now use a cantilever brake saddle and connect it to the main shifter wire. Hook the loop over the brake saddle. Now when you shift, the wire from the shifter is pulling the saddle which in turn pulls the wire that connects to both deraileurs.

Does that make ANY sense? PM me or call 831-521-3801 and I'll try to clarify.

I like your thought process. I tried something similar with an attempt on the brakes but I believe I tried to make it too complicated. I don't have a saddle as you described but I think I can make something comparable. This method is simple in design and reduces a lot of the headache. I appreciate the advise.

PM me with your address and I'll send you one. I have s**tloads of them!
And I'll make a drawing of my idea to go with it.