Scott. Most ECM-controlled exhaust brakes will not activate unless driving (higher speeds in second gear or faster).
The solenoid that sends air pressure to operate the exhaust brake is just a simple 12 VDC unit. Remove the original wire that supplies the 12 VDC positive and use any other source of 12 VDC positive-- lots of them in the engine compartment.
If there is no connector at the solenoid, install one Protected male and protected female connectors. A $1, 5 minute solution. I would not just apply an outside source of 12 VDC positive to the existing wire-- I don't like "back-feeding" relays/ECM's.