The reason they won't except a waiver is because they will then payroll deduct the WC from a 1099 indepedent contractors check and then pocket that money themselves. They know you don't need WC as an indepedent contractor. It just gives some of them an excuse to rape you of additional money. I've seen it happen.
This is CABL.com posting #198013. Tiny Link: cabl.co/mZFV