OK, here's my version 2.0 idea. Buy the eBay $2 opto-isolator module. But rather than tediously replacing the DC opto-isolator chips with AC ones simply put a 10-cent bridge-rectifier on the screw-terminal inputs of the module. No soldering required!
You'd still want to put a capacitor on the DC output side to smooth out the 120 Hz pulsed DC so that the relay module doesn't chatter or buzz. As GRJ suggests, something like 10uF or so ought to do it.
