a two part switch would be a good idea. like a tggle switch and a button so you don't bump it by mistake in the freeway.. I'd put the button in where your traction control stuff is. under the radio. and maybe the toggle over your feet or in the glove box. there's also that ash try thing i always use as a cell phone holder.
Use a push button swith, the steering wheel or ebrake is a great place for the button. I'm so sure about using a toggle as you want to be able to release the button fairly quick rather than flick a switch, and even if you touch the button on the freeway it shoudn't matter unless you are on the brakes and havea bit of brake pressure. . I've got mine on the ebrake, but may move it to the steering wheel. The e-brake is great if you have a 6spd and want to use it to stage the car, or use it for inclined stars.
Mine mounted under the ebrake, easy to release the button and move your hand straight to the shifter for the 1-2 shift after staging the car.
In a 6 SPD I am curious how mounting it on the cruise control or high beams helps with your hand position at the track, especially if you are using the line lock to help stage the car, seems like a lot of movements to get one hand on the wheel and one on the shifter if your reaching in this area, but I've never tried it.