1. Weigh your heat shrink using a postal scale.
2. Use this calculator to figure out how your balance changes:
To use the calculator, you will have to fake it out because it wants to deal only in discrete weights (a small chunk of lead, not a long handle wrap). Tell the calculator you are taking the entire weight of the heat shrink and placing it at a single point whose distance from the butt (L) corresponds to 1/2 the length of the heat shrink.