Unfortunately, my 35-yr experienced and trustworthy repair guy reported back to me that he had tried your suggestion, but found that the GM designers - in case of failure - had designed the system to default to the window unfreeze position...which probably makes sense for a colder climate, but not for soCal.
So I'm stuck with either living with the window flow for hopefully several years yet, or biting the extensive labor costs of removing and replacing the dash in order to replace the dead actuator. Since I can afford it, and my PA has only my 74K miles on it, I've chosen the latter.
But thanks anyway for suggesting a solution which, except for the default design, should have worked. c'est la vie!