your remote pager hopefully has an AUX button. just program that to trip a relay, a relay that actually opens up the switched lead to your power supply. that way, you can start your car then activate the AUX which will disable the computer until your turn the key (turning the key resets the AUX mode so the relay reconnects the switched lead). the 791xv system i have has 3 or 4 aux buttons actually, i can do basically anything i can think of if i wanted to..
if youre saying your computer starts with your engine right now, and you dont want it that way, just hook a switched 12v line to your REM input on your power supply. preferably, the switched 12v right from your ignition.