While on the surface the heavy prop nuts and prop washers seem like a good idea and it does get the weight further forward than some methods, I just cannot help but think how this cannot be good for an engine running and flying at the same time.
The extra gyroscopic effect in flight (worsened if you use a larger prop, also a way to get extra weight out front) would be combined with the extra weight to shorten the life of the engine.

The extra battery pack idea is much more favorable but may not be enough. Any possibility of lighteninf the other end of the plane just a little? A little can go a long way. Often a third of an ounce lost in the rear can mean one ounce less to add up front.

Good luck, Robert