I think that should be OK. You don't want corncob to swell inside cases, or it will get stuck, but mineral spirits won't swell it as much as water does. Try just a small capful at a time, checking every hour. I know a lot of folks add that small amount to tumble just to wake the polish up a little.
Gunsite Orange Hat Family Member
CMP Certified GSM Master Instructor
NRA Certified Rifle Instructor
NRA Patron Member