I work for Volvo myself and they either use Bosch or Marelli ETMs. I have seen the same ETMs fitted to loads of vehicles including Lambos and Ferraris. Some of the ETMs Volvo use are software controlled and will only work once the relevant software has been loaded into them. These are the ones that receive the signals over a CAN bus system. There are also some that just receive a voltage signal direct from the engine ECU to control throttle flap which I think are going to be more suitable to you.

I will try and get the pin specs for you tomorrow so you can see what the ETM's are seeing from the engine ECU and accelerator pedal inputs.

Have you thought about running a small electronic vacuum pump connected to a vacuumed controlled flap as found on most modern diesel intake systems? The vacuum/flap could be controlled from a vacuum solenoid which would give you the fully open and fully closed positions you are looking for.