After posting this I decided to go out and cut the green wire leading to the PAC OS-4 and tie it into the yellow wire for the bypass. It worked! I tied the green wire (parking brake), yellow wire (the "mute" wire for the bypass), and red/white wire (parking brake wire for the PAC OS-4) together and ran it to the HU ground wire. Didn't have enough time to take it out on a test drive yet, but so far it is working.