A brace will work, as long as it's fairly steady. A tripod is definately better though. But I found out about the slow shutter speed by accident. But when you think about it, it makes sense. 1/25th or 1/50th of a second is still pretty fast, and birds are not always moving like little bullets. They move, then they stop, then move some more, in jerks too fast for our eyes to see, but that's how they move. So on high speed burst modes, the odds are in your favor that your going to get some good clear shots and some blurred ones. In my own test, 6 out of 10 turned out good. 
Now, nobody would be crazy enough to do this in the film days and that's why nobody thinks to do it with digital, but hey, digital is free, just bin the blurred shots, no harm no fowl. Well, unless your shooting ducks. 