Cell phone as data feed to wireless router
You could connect the cellphone to one of the computers connected to the network, and have that computer act as the internet gateway
Since it's an emergency situation only, I would tether the phone to my desktop PC, and then bridge the Wireless and Ethernet adapters together, so that the desktop would become the new gateway.
I have also sold Netgear routers that have a USB port which allows a standard 3G USB stick for a backup connection. This may be a possible solution too, though I'm not sure how the tethering side would work.