I've always used a "third hand", but in a pinch just about anything will work, like a piece of chord to tie the calipers tight against the rim. For cutting I use a Park Tool cable cutter, it does a decent job. One thing I do all the time is to dip the cable end into nail polish, I found this to work really well especially when inserting it into salvaged cable housing.
http://dl.dropbox.com/
The nail polish keeps the individual wires of the cable from catching into any imperfections of the cable coils. Later I add another coat or two just for looks.
Carlos Ovalle
Long Beach, California, USA
http://www.ovallearchitects.com