From this;
http://www.sheldonbrown.com/cribsheet-spacing.html

It would appear that you could likely start with a campy 8-speed casette, disassemble the casette and carefully grind the spacers from 1.9mm down to 1.7 mm each to achieve the same 4.8mm cog+spacer deminsion, total width 35.4mm so as to work with shimano shifter+derailler.

Or, you might try using your shimano shifter+derailler on the campy spaced casette by attaching the derailler cable with SB's alternate B cable attachment; http://www.sheldonbrown.com/dura-ace.html This will in effect increase the movement ratio of the rear derailler so that it travels slighlty more per given amount of cable pull, help the dereailler cover the wider spacing of the campy casette. If this results in too much derailler travel, try attaching the cable somewhere inbetween the full B routing and the original routing for an intermediate travel setting.