Matt
Theres no way of sharing the dongle while catalyst is running... you would have to start catalyst on the mac-mini AFTER switching the dongle.
One dongle = One software licence!
There are a number of KVM and USB switched that support USB devices, including a dongle. However its not a good idea because catalyst will revert to 'demo' mode if the dongle is removed - which could happen in a KVM scenario...
If you want a LIVE backup - you need a 2nd software licence dongle...
Out of interest - how many users loose macs during their shows...
Am I just lucky?
Simon