Fantastic idea!
For another layer of technical awesomeness, I'd suggest using micro-suction tape to hold the phone in place:
For folks unfamiliar with it, microsuction tape has microscopic sized suction cups to adhere to objects placed against it...Which means it will hold the object securely like you're using tape, but is reusable because they're tiny suction cups!
[ame="http://www.amazon.com/Sewell-Direct-AirStick-Microsuction-250mmx300mm/dp/B00ITX9OU2"]Amazon.com: Sewell Direct AirStick Microsuction Tape[/ame]