Looking at the wiring diagram, I believe there's a problem adding a second AC power source, in that the fan that cools the condenser is only going to respond to the controller.
It'd be a lot easier (and low risk) to simply connect the two sides of the thermostat to the "Cold Side" relay on a controller and let the controller mimic the thermostat function (set the AC thermostat as high as it'll go)...
Cheers!
[edit] If that's literally a five-position switch that can be set to run the fan - only - all the time, I suppose you could wire in a second pigtail with the black (hot) wire (on its brass contact) connected to the "COMP" C node, the white (neutral) wire (on its silver contact) to the wire labeled "BLUE OR WHITE (N)", and the green (safety ground) wire to the chassis or the wire labeled "G/Y OR GREEN". Then plug the added pigtail into a controller and you should be good to go.
But...that's a lot of work compared to simply bypassing the thermostat...