murray, my answer to your OP has been worrying me all day long...........
Skin metastasis from bile duct cancer is very unusual and it would be interesting to know what the histology of these skin lesions show.
The ear problem could be a metastasis in the skin of the ear, eroding bone OR direct metastasis into the bone.
Does it matter?......YES. if it is in the skin eroding the bone, then Prolia will have little to offer for the pain, BUT if it is a direct metastasis into bone, then it may ease his pain.
Discuss it with your Dr, but the rest of my answer remains.......