So, rooted around in shed and found a bag of Bosch 5 pin relays. Found a 4 pin but its Chinese and I think the Bosch are better.
Plan to wire the new pump through the relay with the ground being made in the emm when the relay is powered. Hopefully this will trick the emm into not sensing the true load of the aftermarket pump. Would like to power the relay from the stock harness wire that powers the pump so the shutoff lanyard works. Well that's the plan anyway. Dunno if it will work or not.