jasper report how to slide up text fields in summary band when one is empty?

jasper report how to slide up text fields in summary band when one is empty?

I have a jasper report for an Invoice. At the bottom of the Invoice in the
Summary Band, I have a few fields which are summed from the Invoice
details. Standard stuff. One of the fields will be a "Account Balance",
which lists any outstanding balance on the account so I can add it to the
"Amount Due Today" which is the last line of the Summary Section.
However, most accounts don't have an outstanding balance so I'd like to
skip the line on those invoices, but move the below text fields up.
How can I accomplish this? Using latest version of Jasper and use the
Groovy engine. I'm thinking I could somehow programmatically change the
position of some elements, or perhaps use a subreport for the summary?