Here is an easy solution. Use an Ultegra 10sp cassette with loose cogs except the last 3. In between all of the loose cogs put a .2mm spacer in addition to the included spacers and the built in ones on the first 3. The .2mm spacers can either be bought somewhere or can be cut with a sharp knife out of stiff plastic sheets using one of the included spacers as a model. Voila! Campy spacing on a Shimano cassette. The last 3 won't be perfect, but it isn't off enough to matter, .4mm, plus the limit screw will force the derailleur onto the last cog anyway.

edit: one thing to add though is that this works with an 11 speed Shimano freehub, not 10. A 10sp freehub isn’t quite wide enough for the spacers. Most recent ones are 11 anyway. If it is a Campy wheel the space is there. I made this setup work on my trainer that came with an 11sp Shimano and i ride Campy 10