You shouldn't have to load a wooden plug. They are usually built to swim to the spec's and weight you see. What I mean is they are already balanced. If you add weight to a plug that swims good already you'll probably make the thing swim like shit or not at all. If you want a heavier plug your best bet is to by one.
Some plugs are belly some tail or head weighted. It all depends on the style and how the plu is supposed to be oriented inthe water. You also need to adjust your weight to the type of wood your using. I quess