Probably pointing out the obvious.....(attempt at humor follows)
Use dynamic balancing. Just pop the thing up there and let run up to speed in about a 70 mile an hour wind. It'll balance itself dynamically. Probably end up with three very SHORT blades..... (end of attempt at humor)
A co worker used to fly copters in the early days of their use by the US Army. Those blades had little aluminum trim-tabs on them that had to be bent up or down to properly balance the lift on the blades. They would go out there with the chopper running and hold up a broom (bristle end up) until it just touched the lower running blade at that trim tab to adjust it. This always sounded to me like it would have the opposite effect of what they wanted, but he swore that's how they did it.
Perhaps such tabs could be used if the lift on your blades does not match. It wouldn't help with the weight issue, but it might help if blades had differing lift characteristics.
Eric von Kleist
Spartanburg, South Carolina