I usually try to build a weight box, or at least a blind nut I can screw sheet lead to, inside where it doesn't show. If you have rear servos you're gold. I use electrical tape to fasten pennies or flat leat weights to the servo box (works for lateral balancing with the aileron servos, too). I have shimmed lead between a tail-wheel bracket and the fuselage . . . faired nicely it looks almost like it was intentionally designed that way. Or, with a nose wheel model, added a lead skeg at the tail. The farther back you can get it the less weight you need to add. It is always worth trying to accomplish balance with the battery pack. Adding no weight at all is the best solution.

I cast lead round balls for muzzleloaders and it is handy to be able to carve a mold as needed out of wood and pour the lead to any size and shape I need.