Absolutely.
All you need to do is adjust your alarm thresholds using the "Set Thresholds" command. If for example if you have 10 working phones on a controller and you want to create an alarm condition simply:
Busy out a single set, "Busy extension XXXX"
"Set Thresholds lines nil 10 nil"
What this does is it tells the controller to generate a major alarm condition should 10% of your lines not work, since you busied 1 of 10, that criteria is now met.
Any threshold will do, but I find trunks and lines are easiest to manipulate and cause little, if any, effect on the customer.