I did the thermostat mod from the wortomatic site for my son of fermentation chiller. Granted, it doesn't have a relay, but the remote thermistor works great. I tape the thermistor to my fermentor and cover it with a folded paper towel. Now the thermostat reads within 1deg of my fermometer. I don't see why you couldn't just add an SSR.
(FWIW, after much bitter experience, I've come to the self-realization that I like to build stuff myself, even though it usually costs more in the end. To be completely honest, I think I may enjoy building the gadgets more than actually brewing. Brewing is just an excuse to design/build new toys...)