The in-line lock is the easiest, just a matter of turing a "T" valve style.
Unfortunately the switch/valve has to be fairly accesable, ie under seat, on the tunnel etc. This may be easy to find by a prospective thief.
I wondered about this as well, but doing it a little more tricky. I have line lock or "roll control" on my Notchback for drag racing. The system is fairly simple; put your foot on the brakes, push the button and hold, take your foot off the pedal and the front wheels are locked until you take your finger off the button. Wicked burnouts are much easier this way.
Now could you take the same technology using a Hurst or Mallory "Line lock" and instead of a momentary style switch use a positive on/off switch. Of course you would be required to have 12v running to the solenoid in order for the lock to hold, (battery drain?) and would the solenoid be able to stay locked for long periods of time? Maybe it won't work, but if it did, think of it,you could hide the lock button almost anywhere inside your car.
Obviously, kill switches are easy to hide. An electric fuel pump has a switch you can hide, battery key,....etc.
Good luck.