I understand wanting to stick with what you have. I just scored some levers so I could avoid going aero on my LeTour IV.

Another thought just hit me...

Some interruptors can be set up to be used without other levers (basically similar to flat bar levers, only reversed).

If you set up the existing levers, and cross levers that can be used without other levers needed, using the cable doubler you might be able to do what you are looking to do.

It seems like it should work, but I have obviously never done it.