I was under the impression that Quirrellmort's zombie-time meant that the Quirrell host-body had been lobotomized. If so, any intelligence that Voldemort can bring to bear is already native to him. Of course, there is that comment in one of his early discussions with Harry about never being able to fully disentangle the mind from the body that it wears...I'm not yet entirely sure what to think about this. I don't think we have any direct evidence that Voldemort can step out of Quirrell without great inconvenience.