Compustar appears to have a hot/cold start function that sounds like it would do what you are looking for.
Here is what their website says about it:
"The hot/cold start feature is an optional feature in Compustar units that will allow your vehicle to automatically remote start when the temperature reading in the vehicle cabin reaches a set temperature. For cold start you can set the vehicle to start at:
For hot start you can set the vehicle to start at:
The Compustar unit will attempt to read the temperature in pre-set intervals; if it reads a temperature below the cold start limit or above the hot start limit the vehicle will automatically remote start. The run time for this remote start will be 4 minutes for regular vehicles, and 8 minutes for diesel vehicles. The set temperature and time interval between readings can be changed by the dealer/installer. This feature may require extra installation and equipment."
I have no direct experience with this system, but found it when searching online.
Seems possible that you could set your AC on full blast. Then when the temp gets too high it starts the van and your AC will run. The only downside seems to be the 4/8 min runtime, I wonder if that is configurable by the installer?
New Van: 2000 Ford E350 SMB RB42
Old Van(sold): 1995 Dodge B3500 SMB RB33