I have heard (haven't tried it) that if you
(1) leave the vehicle in neutral (set the parking brake, of course!)
(2) exit thru the *passenger door* instead of the driver door
that the car will not turn off.
(this was mentioned in the "use your vehicle as emergency power source" thread)
Also, if you just leave it on and it turns off, you should be able use the "mychevrolet" app to "remote start" the vehicle after it times out and turns off (which will start the A/C up at the last setting it was on). I think that you can only "remote start" twice per "park session".
From the manual (this pertains to using the key fob "remote start"):
Extending Vehicle Run Time
The vehicle run time can also be extended by another 20 minutes, if after 30 seconds and during the first 20 minutes Steps 1 and 2 are repeated while the vehicle is running. This provides a total of 40 minutes.
Use remote start to heat or cool the interior when the vehicle is plugged in to maximize electric range by utilizing electricity from the electrical outlet. Normal operation of the system will return after the vehicle has been turned on.
1. Press and release Q on the RKE transmitter.
2. Immediately press and hold / for at least four seconds or until the turn signal lamps flash.
. The RKE transmitter is in the vehicle.
. The hood is not closed.
. The hazard warning flashers are on.
. The malfunction indicator lamp is on.
The remote start can only be extended once.
Conditions in Which Remote Start Will Not Work
The remote vehicle start feature will not operate if:
A maximum of two remote starts, or a single start with an extension, are allowed between ignition cycles using POWER .