Adventures In Nail Biting

It occurred to me about 6 months ago that I had not trimmed Zachary's nails in ages.  I couldn't remember the last time I took the nail trimmers to his little hands.  So I called him over to me, expecting the need to get the hedge trimmers out of the garage, and was stunned to see that Little Stink had taken to doing this task all by himself.  Without the nail trimmers.  He'd plainly been biting his nails, as they were bitten WAY down, past the quick, and he'd taken to chewing on the skin AROUND the nail too.  My first thought was YUCK, then OUCH, then "What kind of Mother am I?"  So off to the doctors we went.  She proceeded to give him a lecture about how much dirt was under his nails, and how he could permanently impede fingernail growth, how important his nails were, etc.  All Zach heard was "Blah Blah Blah".  It had no effect whatsoever.  
I started keeping an eagle eye on him, hoping to catch him in the act.  I caught him doing all sorts of things, just not biting his nails!  Apparently, this is happening at school.  It seems he gets "bored" at school, and can't find anything else to do other than feast on fingernails.  So I started sending activity pad and books in his backpack.  Same result.  Nails down to the quick.
Last week I discovered a product called Thum at Walgreens.  It's a nasty tasting brew you paint onto your child's fingernails.  Then when they go to bite the nail, they're greeted with a disgusting taste.  We're doing this with some degree of progress.  I even went so far as to buy a bottle of "Radioactive, Glow In The Dark Piggie Paint."  I have promised to paint all his nails with this amazing bottle of fun just as soon as I see some white on all fingers (and toes - have I mentioned those are a problem too??)  So I call out to you, my fellow parents.  Have you any wise words of advice for me?  Have you got a nail biter?  Are you a reformed biter?  I'm looking for anything.  Anything that will help the little guy out.  I can't imagine he's stressed out.  Seriously...what could he stress out about?  He's seven.  Help!!!!