Magnum 318 info

Here is a pretty good explanation of how an RE shifts. Basically, it is a electric over hydraulic system (if I have the terminology correct).

http://www.atraonline.com/gears/2006/2006-07/2006_07_22.pdf

Looks like all you would need is a system that can measure road speed, monitor the governor pressure and control a solenoid to cause the governor pressure to rise as required.