Hi Nancy Yes, this is doable, but only if you expose the vaulted rafters to install the venting.
With a ridge vent and open soffit vents in place, I rip 3/4" pine into 1" wide strips and tack these up in the corner where the rafter meets the roof deck. I then tack 3/4" rigid insulation up against these, the width of the space between joists, from the soffit to the ridge. This provides a ventillated chute. I then fill the remaining space with batt insualtion, then put the drywall up over the rafters.
Now, you have great insulation and ventillation.
I don't use the thin styrofoam chutes....as these provide a much smaller ventillated area behind the roof deck.