My first thought was to use the derale grounding wire to send a ground signal to the wire between the ECM and GM relay. 2 problems, 1 I don't want to damage the ecm, 2 if the GM relay is failing or fails in the future the whole system is dead in the water.
LATECH, do you think you could just quick sketch up the bosch setup you just mentioned? It sounds promising.
The gm ecm would not be damaged, and if the GM relay quits, there are several others under the hood you can swap out to get you home, like say the foglight relay, or DRL relay, or god help us... the AC relay.
The circuit is designed to supply a ground, you would have to do something pretty wrong to hurt it.
The bosch diagram... use the same diagram as in post number 4. Ignore the ecm, run the red(ground) the the relay coil, just like in the picture.
Use the derale controller to trigger a relay coil and not some power hungry fan motor. Let a disposable/dispensable relay do that job.