Ability to marshall a header record after writing unbounded detail records

[cachemoney]

Hi,
I've been going through all the unit tests to cover my unique use-case. In my processing loop, I would be planning to run Marshall.marshall to be writing detail records, line after line. Once that is done I need to write a final record(Like a header) at line:1 that has some calculated values. I was looking at writing a test using only_sub_records.def.xsd ,but It seems that the header element object cannot be null when it's time to write a OnlyChildrenContainer.

Is there a way to be able to write a final record at line number 1, after all the body as been written out?

Thanks!