need hidden field in form sublist

I have the following suitelet code that produces a list of item fulfillments with a checkbox next to each.  I need the user to be able to check any or all of them, and then when the submit button is clicked get the list of which ones were checked.  This all works fine except that I have to put the internal ids of the transactions in the list or they won't be available to the code receiving the post. There are other data I'd like to pass through the line items too and making it all visible will be messy.