Thieves aren't the brightest folks in the world. My guess is they'd have no idea what an S&S coupler was, nor how to disconnect it.
If you're really worried, I'd have the builder who installs your couplings provide some mechanism for securing the front half of the bike. Perhaps a small plate gusset between the head tube and the top or down tube. Drill a hole in it, attach a padlock through the hole and then run a cable lock back to the lock that secures the back half of the frame.