You would need to create an extension, probably best for the
module/cron/manage.php and the
templates/default/cron/manage.tpl. In the php file, take the table retrieved from the
Cron::manageTable(), loop through it making a new table. For each record you would use the invoice number to get the invoice record, take the total from it and add it to the
manageTable() row, creating a new array of records to then store in the DataTable. Now you would have the value to display on the screen by adding it the the table heading and DataTable info in tpl file.
You do this as an extension so the code can be preserved when new SI updates are loaded.