Well, I read somewhere that 328s have the battery under the hood so that wasn't a surprise. When I was running an power wire for my HU, I ran it right next to the wire that goes from the battery in the trunk. Since I wanted to make it look even better and come in the the fuse box, like it was done at the factory, I searched high and low for a good hole in the fire wall and all I can say is that there simply isn't one, at least one I found.
You can try finding the hole that other e36s used to get under the hood with the battery wire. To find it, you would have to remove the main carpet that comes up to where the passenger's feet would be. It is pretty high up, just close to the end of the carpet, but I would think that it is sealed completely.
You got a real interesting issue there. I know you can't run it with other wires because they are sealed completely with the rubber gormet and there is no way of getting around that with a coat hanger without ripping it. Maybe you can get by the fire wall where the AC lines are or where the system gets air from the outside. I don't know, sorry man, I can't help you there except for saying that you will either have to be very creative or drill a hole in the fire wall.
