A few hundred years ago when I was still training in the RAF, we visited Preston Centre as it then was and saw the triangulation sit. room. The controllers there were very keen to get us to do Practise PAN calls and follow up with a complete practice diversion. I did it a couple of times and it worked very well.
As soon as they had me idented, they put me onto a discreet frequency to avoid blocking 121.5, however.
These days any 121.5 call is picked up by sattelite and it may be that the triangulation system is getting overtaken by technology in any case.
FC.