I had this issue also with a 3wt 10' czech rod. None of my 4wt reels would balance it. Made my forearm ach after a few minutes nymphing. I ended up sanding down the cork butt so that I could slip on a 3/4" piece of PVC tubing with an end cap. I filled the pvc tube with tungsten powder till the balance point was about an inch from the cork handles grip 'hump'. I then sealed the tungsten with a balsa plug. Slipped the assembly onto the end and epoxied it the cork. Even with the added weight my arm and wrist feels much much better. If you think about it, when it was out of balance, my forearm had to counter it constantly. Now the pivot point is nearer to my wrist, and the weight is actually supported by my entire arm now.
I may go further and replace the PVC with a screw on extension like this....
http://reelseats.com/shop/index.php?...roducts_id=436
Put a fighting butt on it, and fill it with tungsten powder like before. This way it looks neater, and I can adjust the balance point.