Hi nematoad, did you get anywhere? I'm now faced with the same issue and (obviously) looking for solutions! At the moment I'm considering extending the roof over a box consisting of vented sofits and fascia boards.
Read more: https://www.diynot.com/diy/threads/venting-a-flat-roof.7063/#ixzz65NLM43Xl
Read more: https://www.diynot.com/diy/threads/venting-a-flat-roof.7063/#ixzz65NLM43Xl