I was thinking about this potential security risk as well. If the other half connection is done via USB it might be even worse since data will probably be loaded or maybe even run automatically from the storage on the back plate.

You could get a similarly colored back plate, prepare it and swap it with the one on the target phone when no one is looking. The owner might not even notice. That way you can later swap it back and retreive saved information if you don't want it to have to send it via any networks.

This would essentially be the case if the connection is USB, with the added benefit of an autorun to exploit.

Certainly the security aspects shouldn't be ignored.