Can you somehow add cast iron wheel weights? I prefer using them to adding fluid/calcium. No corrosion, however, if the rims weren’t designed for weights then they may have to be reinforced around the holes where the weights are attached. If none can be found, and you are handy, you may be able to make your own from concrete and then paint to match. For example, a steel pipe ring filled with concrete and mounting studs set at the correct pattern via a plywood template