There are lots of commercial devices to help but they can be expensive and often don't work very well.
I came up with this after seeing a similer device in a catalog for $80 and thought I could make it cheaper.
You will need:
1) A Sonicare or other sonic type toothbrush (You may be able to use other types of electric toothbrushes I just happened to have a Sonicare)
2) A single slat from a vinyl mini blind
3) A rubber band
Step 1: The Parts
Cut the slat about 8 inches longer than your toothbrush.
Step 2: Using Your Device
The seed will march down the "V" like ants at a picnic.
Step 3: UPDATE-Adding a Bulk Hopper
After some pondering (and a raid on the junk drawer in the kitchen) I came up with this.
I got a small funnel, cut off the handle and taped it to a piece of mini blind slat.
You could use hot glue also.
I drilled a small hole, in this case 5/32", in the funnel to allow it to slip over the metal vibrating tip of the toothbrush.
A litle bend in the mini blind slat and a zip tie, done.
click thru the images below for detail.