Using an Airport for Streaming with iPhone connected to 3G for Data?

Hi there. I'm currently working in a remote location that does not have access to a WiFi network. I have power, and 3G coverage, so I would like to stream music from Pandora and Spotify to an airport express from my iPhone, using 3G as the internet connection. The trouble is, the WiFi network created by my airport express doesn't have any connection to the internet. So as soon as I connect my iPhone to the WiFi network, it loses its ability to stream from Pandora/Spotify.

Is there any way to set the airport express or iPhone to know that it's not getting an internet connection from the WiFi network?