Take a page out of the local paper, and make sure the crease is very sharp. Then pour the mix on the paper, and gently tilt the crease into a container, and let the lead shot roll off the paper first into the container. You may have to do this a couple of times, but you will reduce the amount of powder in the lead mix on the paper each time, until all the lead is separated from the powder. The trick is learning how slight an angle you have to use to get the shot to roll and separate from the powder.
You might draft a second set of hands to help in holding the paper straight while pouring the shot out into the container. The tight crease tends to grab the powder granules and make them less likely to pour easily, while the round shot heads to the container. If you were into Japanese Origami, you could make a series of fold with tight creases in the paper to separate the shot from the powder.