Not hard, I take it your 8L is a 2000+?
So it doesn't have an ignition on feed to the HU. All you need to do is wire one in from the fusebox. It is the fuse denoted by "Radio S-Kont"
Just wire tap the feed from this fuse (the side protected by the fuse) straight to the red power feed on the Sony. The Sony will have both the yellow (perm live) and red ignition feeds wired together, so you need to extract the red one and connect it to the new feed. This will give you a proper accessory feed that will stay live until you pull the keys out.