I have no idea how the servo motor you mention works. I don't suppose it is likely to be very complex and probably you could create your own controller once you have worked out what sort of signal it needs.
Have you considered leaving it controlled by the existing CDI ignition system (with the HT side isolated or neutralised somehow) and simply add your own separate ignition system to do the actual sparks?
Is what you're proposing to do actually legal in your jurisdiction?
This is great idea, and that will be simplest and for me best solution, and I think that it should work.
Do you have some link where someone already did CDI for 2 stroke, one cylinder bike?
And, yes this is legal, because I'm >18.