It would somewhat depend on how good the ventillation is in the attic on its own. Do you have enough surface area for the soffit vents? What about gable vents? A ridge vent?
One thing that surprised me as to its effectiveness was a radiant barrier stapled to the underside of the roof joists...it lowered the attic temperature about 30-degrees in my NH townhome. This is simply a craftpaper covered with aluminum foil. The version I have has fiberglass filaments to reinforce it. After putting this up, the upstairs ceiling was the same temp as an interior wall whereas before at the end of a sunny day, it was decidedly hot.
In the winter, snow sits on the roof 4-5 day longer than my neighbors, since it also reflects interior heat back into the room. Being a condo, I couldn't put a hole in the roof to install a fan...this seems to work, and it is entirely passive. Worth a try.