Arrange sales order lines for printing invoice

We have a strange customer request. They want us to arrange the invoice detail lines in a specific sequence for them to easily check the info. For example, the sequence needs to be item number, then freight, then discount (if applicable). I tested the invoice print is based on the sales order line numbers, hence now all i need to do is to figure out how to somehow arrange the line numbers. During entry of new order lines, we can somehow change the line numbers to accomplish this requirement.

But the problem arises when we have an open order, and there is revision made to the order. System automatically assigns a new line number for the newly added detail, and for the existing lines we would need to cancel the lines off (to create a new line at the bottom using a specific line number). This is very cumbersome to do on a daily basis.