I want to invoice several sales orders at one time, but be able to show totals under each sales order's items. I am able to add multiple sales orders to the single invoice and create a header above each grouping of items, but want each grouping's (sales order's) sub/total to show prior to the entire invoice's total. I hope that makes sense. How do I accomplish this?

Example: 

Item 1   $3

Item 2   $13

      Subtotal: $16

Item 1  $9

      Subtotal: $9

      Invoice Total: $25