You'll need to run an external/aftermarket sensor/switch on the engine. ECM reads oil pressure directly via an analog 0-5v 3-wire sensor. Its not a standard type varistor, and its certainly not just an on/off switch.
ECM sends oil pressure reading to cluster over the databus.
So basically, no, you arent going to be able to "tap into" anything existing on the engine. Use a second aftermarket pressure switch that closes at 20 psi or something. Im sure Summit Racing has them.
Ben