I know next to nothing about ejector seats. But here on planet earth almost a quarter of the way through the 21st century, the bar for something to be described as "complicated" is set pretty high, especially in the electro-mechanical world.
As ASRAAMTOO has alluded to, the starting point is that both seats can be fired independently (and the rear can fire the front), so we are not starting from a blank sheet of paper. If it is truly too hard for MOD to procure a fix, perhaps the necessary technology might be found in the airbag controller from, say, a Ford Fiesta: anything post 1998 should do it......