Claire,
 
Each ferret seems to respond a little differently to punishment and therefore
your approach will have to be somewhat tailored to its personality.  The
biggest common denominator is consistancy.  *Don't* let it nip without a
"punishment" of some sort.  You mentioned that it goes hyper with a nose
thump.  That's usually a sign that nose thumping is *not* appropriate for it
and may actually make it more aggressive.
 
We've had success with some, just wrapping our hand around its face and
shouting "NO!" each time it nipped.  Some have responded well to scruffing
and shaking back and forth rapidly (not too violently) and shouting "NO!".
 Be sure that you don't put them down after a nip or they'll quickly get the
idea that a nip is how you ask a human to be set down.  Continue to hold
after the punishment.  Offer it a finger or hand to bite again.  If it does,
repeat the punishment.  Keep it up until you don't get the nip and it settles
down with a big sigh.  Then praise it and give it a treat before setting it
down.  BE CONSISTANT.
 
Good luck.
 
Dick B.
[Posted in FML issue 0991]