I've had good luck with a deadblow hammer and wooden dowel. For smooth-bore bushings/thimbles, I use a dowel that will fit inside. For the threaded ones, as Cagey said, thread in a bolt or even the bridge mounting stud itself and use a larger diameter dowel and beat on that. Do make certain that the hole in the body is cleaned up and ready to accept the bushing. If there is an accumulation of finish inside, the ID will effectively be too small and finish/body damage may occur.
One day I'll have a drill press in the shop for such things, but until then, this has been working for me.
Of course, for $10, the Warmoth installation ain't such a bad option either.