Header row

Good question and interesting puzzle.

I'm not sure how possible would it be to script.

<badjoke>You might want to ask the scripting forum</badjoke>

You might be aware of a kinda hidden table option that allows you to choose if header should be repeated on every column (by default), once per frame or once per page. Unfortunately there's no "once per spread" option.

So, a workaround could be to set this Table options > Headera and footer > Header > repeat header "Once per frame/page", then expand your text frame over the whole spread, and set it as a 2 columns frame.

I'm not crazy about this workaround because I don't really like overlapping stuff, but it's the only way I can think of...