FWIW the first silver-wounds were bass pickups! I think for Anthony Jackson, but they weren't Zephyrs. For a bass pickup, where you don't have glass-filled bobbins or bimetallic pole pieces so that leaves Cryo treatment.
If you're ordering a Custom Shop bass pickup on a budget and can't spring for the silver wire, try having the Duncan Custom Shop Cryo treat the pickup of your choice.