Should be easy enough to do. Get a 'feeler' or roller switch from an electronics parts house... radio shack carries a few.
It is essentially a switch with a small are and a roller on the end. Make a bracket near the parking break lever that allows the 'set' brake to make the switch contact. You may have to play with a few springs or flexible levers to come up with a workable bracket, etc.. epoxy putty may help.
Perhaps even easier than a physical contact switch, a magnetic switch like that used on door/window alarms would be very suitable, and require no physical linkage.. just rough proximity between the switch and magnet. The magnet could be mounted on the break lever, and the switch mounted to a close coresponding adjacent location on the block. 2 or more magnets could be used to allow for play, etc, in the break linkage... set it so that only when the break lever is all the way out, that the switches are not contacted. Attatch the switch inline with a red 12v blinking led, w/ power coming from ignition switch. If the ignition is on, and the break is engaged, the led will blink. The led could be panel mounted right near the ignition switch... A buzzer could also be added / substituted. Optionally, you could also add a nc relay to the starter solenoid circuit, as an ignition cutout... if the break is set, when the key is on, the cutout relay is powered, and opens the circuit to the starter solenoid.. no ignition. Depending on the type of key switches, and how the terminals are wired, you may have to play with it a bit to come up with the desired effect.. but these are really basic circuit ideas, and should be very adaptable to most setups.
A combo of ignition cutout, blinking red led, and a mild buzzer might be a good trio...
Just ideas..
Soundguy
<font color=red>"Now to figure out how to wire in a brake engaged IDIOT
light."