Wireless Networking for Visitors

Hopefully there is a quick and simple solution to this -
We have a wireless network and need to give our visitors temporary access to it. This access needs to be quick to set-up and remove from there laptop.
I'm aware of the ability to use a USB memory key to set up a wireless connection including the WEP key and that these can be removed by manually deleting the connection.
Does anyone know of device that can be set up and then just plugged in to the laptop whilst they are visiting, leaving no trace on the laptop when it is removed?
Your help is very much appreciated.