[Outwest34au]

You need a lockout of either "Steer vehicle/Engage forward drive gears/Release a brake"
If you have an auto behind your LS3 it may be possible to wire in through a master solenoid off your immobiliser 3rd function. I am not familiar with the way the autos in them work so cant say for sure.
Some sort of solenoid activated locking pin along the lines of a reverse lockout solenoid maybe if you have a tremec, maybe a reverse lock-in setup???
A solenoid operated stop on the brakes? Possibly like a line locker solenoid to make the brakes "ON" and unreleasable unless activated by the immobiliser once again. The brake lock would be pretty easy to do.

Even though I am retaining my steering lock I was reading ADR 25/00 - ANTI-THEFT LOCK last night and pondering possible options if you went the other methods.