Try it in slow motion, it's very easy for some people, very difficult for others. It's basically a trick, like stick-twirling, but noisier. There is no relation between drum skill and one-handed technique (IMO). I started fooling around on drums in December, and I picked it up in five minutes or so. A friend of mine is a very solid drummer, and can't get it. The guy that plays drums in the band my drummer friend sings in picked it up about as quickly as I did, and he's not a real tight drummer.
Anyway.
Hit the snare head and rim simultanteously. The snare hit will totally drown out the rim click. Continue moving your hand downward a couple inches, allowing the stick to pivot in your hand, by relaxing your fingers. The stick will start to point upwards. As you bring your hand back up, close your grip, bringing the tip back to the head. The stick stays on the rim until your hand rises above it. Raise your hand up to the original position, and repeat. The trick is to contact the head and rim at precisely the same time, or it sounds pathetic.
There is a really good video out there, but all the likey sites are bant here at work, so you're on your own.
Search "one handed roll"