A time-out might work.  When he bites, just put him in his cage for just
2-3 minutes, and see if it works.  I might suggest to stop tapping his
nose.  It could hurt his nose and create more anger for the ferret, so
maybe that's why he's biting back.  I got pretty lucky with my ferrets,
nip training was easy for all but two.  One, Johnny, I am still nip
training *rolls eyes* he is over a year old already lol
 
He just refuses to learn.
 
Another one, Fonzi, I figured out, was biting to get down (a member of
the FML helped me out with this one!  Thanks again!  He isn't biting
anymore!!) so I let him down and learned to let him come to me.
 
A scuff and gentle drag on the floor might help, and positive
reinforcement it always good.  When he does somthing good, give him a
lick of 'tone, but don't reinforce the bad behavior.
 
Hope I could help a little,
Good Luck!
Krista
[Posted in FML issue 4717]