Document Approval Filter

We would like to use the Document Approval process for sales orders in Nav 5.0 sp1. However, we don't need the process to run on every customer, only select ones. Ideally, we would like to put a check box on the customer card and when an order for that customer is processed, the code would trigger based on that check box as well as the approval amount. Is this possible or is there a more efficient way to handle this? If possible, what code needs editing?

Thank you