Promotional Goods Modifier - Default line type needs to be changed to Bill only

Scenario: for a particular sales order type, I need to insert a default process charges item. The charges item will be a % of the total order amount. For this requirememt, I created a promotional goods modifier. System is inserting the item as expected. But issue is, we need to have the line type on the inserted item to be bill only. But system is assigning the default line type associated with the SO Header order type. Does anyone know or worked on a requirement to change the line type systematically?