The ecu just looks for a load ie the charge cooler relay. This is not hard to add in. And no need to map it out.

If you check the looms there are around 15 differances between Rs/St ecu’s with some work on an St loom you can run the Rs ecu fully functional.

The first thing that springs to mind is the St fuel pump driver modual. Cut the plug of and wire in a standard 40a relay. Add fuel return and upgrade the pump.
The Irmc plug can be chopped of and repurposed for boost solenoid and charge cooler relay.

And so on