I have some bad guys.
I traced the yellow/black wires from the injectors. They all meet up in a single connector next to the ignition coils. They don't meet before the connector like we were hoping. I took apart the connector and all the wires are connected to one another.
Right now the only option I see is to set up relays for all four of the wires. I really don't want to have to do this if I can avoid it.
I'm currently looking into using two DP relays or an industrial style relay with four poles.
If anyone can come up with a better solution let me know. Otherwise I will continue forward on this.