I also had a choking ferret.  Eventually I scruffed her, pryed her mouth
open, and shoved my little finger down her throat until the stuck food went
down.  That was my instinctive response, and I say - whatever works!  She
recovered with no ill effects.  I have also done the Heimlich on my dog who
"inhaled" a Milk Bone.  It worked then, too.
[Posted in FML issue 1374]