Bill to Account Only On for Studio/Not Parent Portal

We would love the Bill to Account feature only be available for the Studio to use in Point of Sale and not available to parents in the Parent Portal. We do not want parents to be able to load up their account with debt and our order numbers to increase when money has not been collected. The studio wants to have the ability though to bill a parent through the store, for example, in the event that the order window has closed for parents, but we have an extra item to sell.