Just a quick point of correction...there is access between the radio slot and the HVAC grommet--that is how I wired my ipod adapter. On mine there was a plastic panel taped in place that hid the grommet from the radio slot, but it comes right out.
Interesting find, I had completely missed that. So, no need to drill a hole. yellowvert, remove the "A" post panel cover on the passenger side by removing two screws inside the cubby hole. Feed the wire along and behind the passenger airbag untill you can see it trough the A post opening. In the corner where the parcel shelf and the side sill meet there is a little rat hole big enough to feed wires trough from the A post area to the under dash area, you could route it around to the vent opening or as I describe in post #25 to the front side of firewall and fish it between firewall and fan.