I never updated this particular thread on this topic but I ended up abandoning this project. The bigger roadblock I run into is that cars are not prewired for it: this doesn't mean it can't be done but it would require a lot more work that I'm willing to spend on this.

You'd basically have to recreate the whole wiring: based on WDS there are some connection in the front of the car, some in the trunk, then run the wire to the pump under the car... Way too much work for me. And after is all done the unknown of the coding remains...