Urgh! That story turned my stomach. That's the one thing I really don't like about power tools... it's all too easy to remove parts, you just don't get that with hand tools (nasty cuts, sure, but everything stays where God put it). I still have and use the things, but they always seem to me like they are just waiting for an excuse to hurt me. There was one thoroughly stupid moment with a cordless drill, an auger bit and my thumb - but it was only a tiny cut and I called myself an idiot for a couple of days after doing it.
As for the guard...
I'd imagine a long box with an internal width of about an inch or so, fixed solidly to the knife (I'd say a wingnut firmly tightened should keep it fixed in place to an elongated slot - allowing height changes if you need them) - essentially something like you already have but tightened down so it doesn't move.
Then a thinner box inside the other, hinged at the back, which lifts up when the wood comes into contact with it.
Of course, that would still allow a hand under it if the fixed box was high enough above the table, but the whole guard wouldn't hinge up without enough force to overcome the grip of the wingnut/bolt.
I've not given it much thought, but the picture in my head seems like it would work - for the little that's worth.
