I’m not sure if I understand properly… I believe that your answer is in my cathedral ceiling ventilation article or this answer to Kyle's question: how to ventilate cathedral ceiling?. Look at the third drawing showing a vent in each rafter space (you’ll need soffit vents and air space between the roof decking and ceiling insulation in each rafter space).
It doesn’t look pretty but sometimes this is the only solution. There’s another type of a vent but I don’t know how steep is your main roof and if it can be applied in your situation. Look at this page – http://www.airvent.com/homeowner/products/ridgeVents-specialtyFilter.shtml