You wouldnt split any sensor signals to run standalone.
And as much as it sounds like a simple solution, its not. The OEM ecu has several potentiometer tracts to monitor pedal position and the fbw throttle position. Simply feeding back a spindle driven potentiometer will leave the OEM ecu confused as to where the rest of the system is. And like I said, you are going to have to match the resistance curves.....unless paul or someone can completely reprogram the break points....in which case your going to be spending over £500 for his time to do something quite so bespoke since the fueling and ignition maps will look so different.
The stock ECU will also use MAP as the main load indicator, not TPS. And when you are running bodies on a speed density setup you end up with half of the map doing practically nothing fueling wise, then the top half ramping up like mental as the mass airflow changes abruptly with throttle opening. So no only are you wasting half the map, but your asking a LOT from the interpolation capabilities of the ecu. If you rescale the breakpoints to make more use of the map, then you'll be having large jumps between mb values in the lower corner of the map and partial throttle/idle will be quite rough. Speed density is only really any good when you have a plenum to average out and dampen the manifold absolute pressure.
Speed density/alpha N blending is another thing, but not on the stock ECU I wouldnt imagine. But then again I dont know too much about the inner detail workings of the stock ecu since I dont mess around with winols or anything.