With a spare fuse just in case, I tested the relay idea. No joy The relay barely triggered, meaning that it did pull the arm a teeny-tiny bit but not enough to pull it fully away from the contacts. The turn LEDs did illuminate.
Maybe I need something that requires less voltage, like a transistor? I know very, very little about making such a switch except that a transistorized switch would likely work.
I think for now I'll just wire in the DRL LEDs. The signal LEDs can be seen but ya really need to look to see them (let's call them "subtle" ), something 99% of the drivers fail to do