There are several installations that are similar to the one you are thinking about on my web site under Installations. There is also a bunch of photos in the Gallery. Perhaps one of these will give you a few ideas. Also, read the VHF Options article.
I don't like trunk lip mounts, period! The coax eventually fails, which causes all sorts of problems. I'm an advocate of drilling the proper holes (especially with a 10 model year old car), and once you have some experience with a trunk lip mount, you'll know why.
I'm with Lon on the relay idea as it causes more problems than it cures. Most newer radios have an auto-off feature, and regardless of the installation, if the radio is equipped with it, use it. Worse case scenario is, the radio will reset when you start the engine. This doesn't happen with all cars, or all radios. As Lon says, if it bothers you, turn it off.
By the way, there is an unused plug in the firewall near the power brake unit. It is difficult to see, and difficult to use, but if you don't want to drill a hole, it will suffice in a pinch.