The "Vantage Connect Expansion Module" is the app that displays the user's programmable buttons (yes, the name is rubbish and makes people think its an extra bit of hardware).
It can be run on the same Vantage phone as the user's Vantage Connect app and both apps have buttons that make it easy to switch between the two. If you have any spare Vantage units lying round, they can run additional copies of the button app for the same user (doesn't need to register to the switch so doesn't need to register as phone).
Its officially supported with the R11.1 SP1, including the necessary extra lines in the auto-generated 46xxsettings file.
I played with it as part of the service pack testing and it worked quite well.
Stuck in a never ending cycle of file copying.