I've gone through a couple iterations on my R1200R. First was a
cable socket, which just poked out from the front of the tank. Not super clean, but worked until I figured out what I wanted. I ended up with this arrangement:
I've since updated how the phone (running Navigon) is mounted, much cleaner and less bulky. The plate and the single RAM ball are all on the top left bar mount bolt. It's mostly Powerlet parts but I had to use a bolt from some GS kit from Touratech to make it work. I think. Might have been some other long bolt I had lying around.
Anyway, I'm working on a way to hard-wire my Spot Messenger and have considered the very thing you're thinking of - putting it in the plastic trim on the front of the tank. I haven't been in there recently, but I think it's doable - there's a fair amount of space in there. Could also maybe mount a small plate to hold the plug up under there, like where the GPS plug is.
You could also switch to one of the
Bags-Connection tank bags that use the powered mounting system, and wire directly to the mounting collar. Then you can have whatever connectors you want inside the tank bag.