My thought was to install an additional octal socket and use the 12v flavor of this guy: http://www.parts-express.com/pedocs/specs/kest-kir2p-series-specifications.pdf
To use this, it looks to me like I'd attach the 12v control feed to pins 2 and 7, the power transformer primary to pins 8 and 1, and the mains hot and neutral to pins 3 and 6, respectively. I would probably also wire the front panel power switch in parallel to the relay so that I could turn it on without using the control loop.
Has anyone here ever added a power control loop like this to one of their projects? Any gotchas to watch out for?
I've never done this, but I did spec out a delayed B+ circuit for my last amp that would not apply B+ for 30 seconds if the power got cut. (It would however apply filament and bias voltage immediately). The whole idea with that circuit was to build in a fail-safe mechanism for the amp because the amp was going into an environment with toddlers running around who like to flip, pull, push, and turn any switches they can find.
I never actually built that circuit because I ran out of room on the chassis, but I'm pretty sure it would have worked. So I was switching the power transformer secondary, whereas in your situation, it looks like you want to switch the primary. I decided to switch the secondary so it didn't require a separate 12V source to run the relay