The easiest retained accessory power wire in a VE is either of the two big green wires in the main harness of the power window switch block.
Connect it to a relay, and then use the relay to switch a +12V feed from one of the constant power wires in the headunit harness - They're orange with a blue trace.
Et voila, you have remote power line that will turn on when the key is turned to ACC, and then stay on with the radio for 60 seconds after the key is removed, or for 5 minutes if the key is in the ignition at the off position.
It turns off immediately when the drivers door is opened (or after the above time out), along with the radio, windows, and everything else that uses retained accessory power.