Assuming the drivetrain is currently all Shimano, I believe the easiest solution would be to use everything you have, but simply rerout the rear derailleur cable via the "Hubub" route, as explained here
A J-tek Shiftmate without a Hubub rerouting would also solve this problem.
I know neither of those two solutions actually answered the question; they just provided potentially easier solutions. So to answer the question... There is ALWAYS a way to do something. It's just a question of whether it's worth the effort and cost.
I'm going to rephrase the question which seems a bit ambiguous with its use of terms. I believe the question is "is there any way to make a Campag 8-speed pre ExaDrive hub compatible with Shimano 8-speed drivetrains?"
This forum thread
presents some good suggestions that could be adapted to acheive the desired outcome. The main suggestion is to go hunting for a suitable non-Shimano, Shimano compatible freehub body that can be swapped over for the freehub body on the Campag hub.
I am no expert on Shimano, but I believe these should be easy to order, since almost all Shimano freehub bodies use the same spline pattern regardless of the number of gears used. They probably are not cheap though.