Two options come to mind from my theatre background.
One common trick is to take a length of duvateen or any other cloth really and cut diagonal slots in the middle of it. Attach both long ends to some speed rail or wood dowel. Secure one with some C-Stands and then the other would be attached to some line going through pullies. You then use the lines to raise and lower the loose end of the cloth which causes the contents to shift back and forther and trickle through the slots you created. This is much easier to make work correctly with some kind of overhead rigging available, but if the shot is tight enough you could certainly do it with just stands and pipe and some creativity.
The other option that requires more fabrication would be to build a drum (much like what you would see for raffle tickets) with appropriate perforations to its surface to allow your material to trickle out of it, a hinged door with lock for loading your material and some kind of axle going through it so it can spin easily. Then hang or mount the drum above and use either a remotely controled motor or rope to spin the drum at what ever speed gives you the best effect.
I am sure there are other options, but thought these might help! Good luck and I'd love to know what you come up with.