And the same for the RV8 if possible!!!!

I recall seeing one homebrew solution that involved a rod for each lever going through a hole and grommet on the side bulkhead. It was connected to each lever near the top with a bolt to a rod-end bearing on the rod. The other end was just a button end for a push-pull control.

Hi Rob,
 
Matt Dralle in the US fitted a rear throttle and prop control to his RV-8 using the Deluxe 2 lever control. It seems to have involved quite a bit of work but it is well documented on his website:
 
http://www.mattsrv8.com/
 
Hope this helps.
 
Cheers,
 
Owen

It was in the US, so didn't get the benefit of LAA scrutiny.
 
 There was also an 'uninstalled' system where the end of a rod clipped onto the throttle handle allowing it to be pushed and pulled from the back seat. Doing that for all 3 levers may be a bit messy.
 
There's less width in the rear cockpit; especially in the RV-4, so I'd favour having push-pull knobs one above the other on the side bulkhead rather than a quadrant where the levers need to be side by side.
 
Is there really a need for a passenger or instructor to have prop and mixture? Maybe formation training in the early stages, but they would struggle to see the engine instruments.