Amount Open on Sales Order (line item calculations & transaction body field)

I need a custom field that shows the total amount open on a sales order for reporting purposes; the dollar amount of items on the order that are remaining to be shipped.

I was able to do this as a custom transaction column field, totalling the remaining amount open for each line item using the following formula, however it wouldn't pull into reports --- the field wasn't available:

({quantity}-{quantityfulfilled})*{rate}

Perhaps custom transaction column fields can't be pulled into reports? Not sure. So I moved on to something that I figured should work. The thought was to create a custom body field and deploy a client script which would sum the totals of the custom column field from all the line items, and populate the body field with that total. It didn't work either. Netsuite would show an error in the custom body field saying something like "Error field not found".