re. spike, I haven't got anything suitable in the house, next time I'm in town I'll look for one to experiment with.
One thought I had is that instead of a washer, one half of a ball would be better - the wider the handle movement range, the larger the washer needs to be and the more it will point downwards at larger angles, making the 'cage' too big and the 'fall distance' to high. A rounded part would be better. But how would you attach it? I'm not sure soldering would be strong enough. Or how about using a long thin screw thread instead of a plain spike, and just rounding off the top? Then you can use nuts.
Good idea...BTW, a drill of the right width, ground to a 90 degree angle on a bench grinder would make short work of creating a shallow and symmetrical recess for the needle part of the stabilizer. I would probably be inclined to make a needle with a very slightly rounded tip so it won't dig into the steel above it.