So I've been meaning to convert my in-dash cup holder into a mobile phone holder.. well at least the driver's side so I'll still have at least one cup holder. Before I start hacking into it, has anyone done this before with an elegant solution? I have no time/energy to think properly.. I'd like to be able to still slide the holder back in.

Note: Currently my wife and I have iPhones (4s and 5) which have the same width. This can be a near-sighted project without planning for future handset sizes..