I had, from what you have discribed, the same problem earlier this winter. Dormers with insulation in the attic restricting airflow from soffit up through the roof vent? Yup same thing. I was able to go to the local home store and buy roof vents, ProVent rafter vents is what I bought. They were about 2 bucks a pop, made of black plastic. You place them in each bay created by the roof frames. Nail or staple them in place and bam you have a vent that will ensure the air from your soffits has a space to go up through the dormer. From what i remember most building codes require at least 1" of space.
I checked my roof in the crawlspace a few days after I instaled them and it was as dry as could be. I'm hoping for a much lower a/c bil this summer as well.
Hope this helped.