I took a different strategy to the balance problem. No criticism implied for your setup, if it works for you then great!

I went with one light per wheel. I fell back on my auto mechanic background for wheel balancing. I used lead fishing weights from a sporting goods store to balance the wheels. They sell tear drop shaped lead weights that you can easily cut into with a screwdriver or chisel. Then you just crimp them around the spokes opposite to the lights. You can fine tune the balance adjustment by how far you set the weights from the rim. Depending on the size/weight selected, no more than four weights needed, distributed over 3-4 spokes. No issues with speeds over 30mph (down a hill of course!) No, thrown weights or shifting of weights. I keep this set up on the bike for about 5 months for my fall/winter commutes. I run the lights on 36 spoke Mavic A319 rims with Shimano XT hubs on a Surly LHT.