Andrew Stewart has it down. Campagnolo needs the same technique as Shimano, except it is easier for some reason.

I like the idea of using a hex key in a bench vice to hold the derailleur top bolt. My only difference in his approach is I use a small (say 3 or 4mm) hex key to rotate the backing plate. I find the L-shape of hex key provides more resistance to slipping than a flat-blade screwdriver. A third hand also is a bonus.