Before I get too crazy on this, I'm simply going to see if the DRL input from the body control module is removed when the headlights are turned on. This is just a voltage that is either there or not. Those of us who did the "DRL Disable" cut this wire to prevent the voltage from getting to the relay unit (I did the DRL disable a couple years ago, but left my DRLs on a switch so I can still control them).
This seems very likely. However, my only concern would be if when the headlights turn on, that would "dead-end" that input for DRLs by the contact of a relay actuating. There are only 4 high current relays on the board, so does that mean one for each corner (turn signals), or one relay per side turn signals, one for hazards, one for DRL? This is EXACTLY why I want a diagram of this relay unit. LOL!