Like what? Power mirror up/down, up/down, left/right, left/right, then honk the horn twice? 
Exactly! Except it's up up down down left right left right Brake Accelerator
The common wires to interrupt are, as mentioned, starter relay, fuel pump, or coil power. IMO, they're all too common, and fairly simple to bypass. Assuming it's an EFI car, I'd go for the signal from the crank/cam position sensor (in this case, the distributor pickup) to the ECU. Unless the thief finds the switch or wiring, the ECU isn't going to fire the injectors, so the car will not start. The best part is, that wire already passes through the dash on our cars, so assuming you've got an installer willing to find the loom, tear it apart, and reassemble it cleanly, it will not be easily found.
As for a hiding place, I'd suggest behind the ash tray, so the ash tray has to be popped out to flip the switch. Another option would be up underneath the dash, somewhere you can stick your fingers in to flip it, but can't actually see it from either the driver's or passenger's seat.
