An out-of-the-box Zen Cart doesn't distinguish between taxable and non-taxable attributes. If an attribute is associated with a product that's taxable, then the attribute is taxable.

As a possibility, you could reduce the price of the Insurance attribute assuming that it will be taxed, bringing the price to the full value. Of course, that won't cover the case where you sell out-of-state and tax doesn't apply (unless CA requires tax to be collected regardless).