If you really wanted to do this, a more secure approach is onion routing. It's essentially the same problem -- attempting to preserve anonymity in the face of adversarial network hardware, while being limited by a requirement to enter / exit through certain nodes.

So you'd want a mesh network, formed adhoc out of currently in range cellular device neighbors, with packets re-encapsulated and encrypted at each hop, eventually hitting the tower from a random device.

Authorization would be impossible (the intent of the scheme) without a side channel (as you can't simultaneously have individual authorization and individual anonymization). Which makes it a non-starter for commercial use.