Secondary Fuel injection/ ignition with megasquirt

To keep the stock ECU in my '01 Forester 'happy' when I turbocharge it, I'm going to run a total secondary fuel injection system with 42lb injectors that will only work under boost while the MAP signal is clamped. It will take machining and welding on the manifold but will be worth it. I also want to control ALL of the cars ignition since the Megasquirt can do that and I need to retard timing under boost.. If I leave the original harness unplugged won't it trigger a CEL? I'm thinking I could wire in a resistor pinned correctly to mimmic the internal ignitor/ resistance which I read is about 1 ohm