ShyT:
"The safest way is how the RAF engineers used to do Chinook ground runs (possibly still do).
They removed the rotor blades."
The last time I called up a Blades-Off Ground Run (on a Mk1 at Gutersloh) it was done by a pilot (well, I think it was a pilot?) who became nervous when I pointed out 80 open Jobcards and a crewroom chair for him to sit on.