AFAIK, it cannot be done.
These event associated with RGD and structures differ from ''standard'' events.
As the engine check for all the structures in the map, there is no specific region defined in the StartEvent ScriptCommand,
The kind of display you mention are code related and cannot be achieved by Scripts.
What could maybe be done is having a message pointing to a region when clicking on it.
You could try that ; http://www.ageod.net/agewiki/GenMsg
Let me know if it helps