Ive got my NexusOne mounted on top of the airvent.. sure my screen isnt as big but power was run from the cigarette lighter wires within the dash and audio is A2DP streamed 
I liek your idea! just need to finish up the base and block out the wires
(i.e. clean it up!!) -> sorry thats the wire neat freak in me!
I liek your idea! just need to finish up the base and block out the wires