Re-order item list in invoices

Suppose I make an invoice with several line items. After I add 3 items I see that I missed out #2. The sequence order is important to me, so I really need to be able to add the new line at the bottom and then drag it up into the correct place in the invoice, but I can't. My ony approach is to cut and paste all the intervening lines so that I make a gap to add the new #2 item.

This is a bit irritating, so if you can implement the ability to drag and drop lines in invoices being edited that would be very helpful!

Thanks!

Mark