I think I may have mentioned this on another thread but putting some extra shims in between the hex and the outer wheels bearing (like DCM said above) will go a long way to fix any issues with the kit hexes.
There are two faults with the hexes as standard:
1. The are a loose fit over the axle which allows them to rock and twist on the pin under the force of the wheel moving around.
2. They are not supported evenly when you tighten the wheel because as you tighten the wheel you are applying pressure primarily to the area of the hex which contacts the pin. Effectively you are trying to "bend" the hex around the pin.
By adding shims between the hex and the outer bearing, you are removing the ability of the hex to move around and when the wheel is tightened the hex will have even pressure because it is now being supported by the inner race of the outer bearing.
Easier to do than to describe
