Its tough to do on the clutch. I've seen a few try to wire it like you say, but all of them have returned to a switch activated either on the shifter or steering wheel. Alot of guys are wiring the 2-step into the left horn button. It requires a relay though since the horn works off a ground circuit.
I know of one guy who tried putting in on the clutch using two separate microswitches. The first was installed on the clutch similar to the safety switch, but with his own custom bracket. Then he also had a microswitch attached to the stop ring on the base of the shifter so that when the shifter was in first gear the switch was engaged. It then took both switches to be activated (shifter in first, clutch depressed) for the 2-step to work.
The easiest route is to go with the AOD like I have. I've just got the 2-step and transbrake wired together off the same switch!
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Jeff Chambers
Trophy Stock #3
11.462 Seconds / 117.43 MPH
Chambers Racing Team