I would like to offer USPS First Class mail, but restrict the weight to orders of less than 10 oz or .6249lbs. Essentially preventing it from being offered as an option for orders with weights of 10-13 oz. I would like to achieve this without having to add a tare, or changing product weights. Is there a way to edit the USPS scripts to do this? Any help with this would be greatly appreciated.

Using Zen 1.3.8a clean.