Well I think you have a pretty good idea to start with James. Create what in OpenHAB terms is called an ‘unbound item’ meaning it is not directly bound to any specific physical ‘thing’. It is a place holder for your display value. Make it a String item. This example would need placed in an items file.
String MyAlarmValue "the value I want displayed" <alarm> (gMyCoolGroup)
docs for items:
here is Rich’s terrific explanation of unbound items