I don't think that will work. The device that maintains the clock (which data is lost if power is removed for too long) is also the device that handles the "auto power-on" function. If the clock data is lost, the "auto power-on" data is likely also lost.
I see what you are saying, hmmm.
I admit I haven't actually tried this in my own car, but a friend running a live feed set his up that way so that if there is ever a power outage the unit will restart on its own. He was under the assumption that if the power was off long enough that it looses it clock time, when you apply power the clock should start at 00:00 and you have the auto-power-on set to come on at 00:05... so within 5 min it should come on.
I think the "auto-power-on" info is a setting stored on the sd card, just like the frequencies/talkgroups, etc. Has anyone confirmed this?
Either way, all the more reason GRE needs to come out with a mobile version that does TDMA and is capable of a remote mounting with a remote head, etc.