The RAF has two plates, one on each side of the upper mast, that the rotor head is mounted to. There are two bolts holding these plates on - an upper bolt and a lower bolt. By shifting the hole fore or aft on either of the bolts will shift the angle of the rotor head. These are the plates I was referring to as the cheek plates. By changing the angle of these plates to lean the rotor head assembly back will change the balance of the hang test.
My guess is that several people have done this, but I'm just not reading or hearing about it. Most I have talked to have just added lead weight in the nose of the aircraft.