We've had this conversation many times before, but I do agree that the type of predestination represented by strict calvinistic groups does get a lot of negative attention. A lot of it is probably unfair attacks, but there are others who simply disagree and do so respectfully.
CS Lewis' idea of an inviolable framework would not violate anyone's free will, but I've had many staunch calvinists agree that everyone has free will. Some are just "so demented" they'd say, that they've got no interest in choosing anything good. They'll only and always choose their way to a depraved life.
Calvin talks about man's free will so I doubt if you can get around the idea of "free will" entirely. When Reformers talk about man not having a "free will" it is in relationship to the inability to choose good. God's Spirit leads us to all truths. As believers we either listen to God's Spirit or follow after our lusts.
I'm sure I've read C.S. Lewis' view but at the moment I have a brain crap. I'll have to research it. But seeing how C.S. Lewis was a Catholic I'm sure it would fit within his paradigm. It does not and should not fit within the Protestant's paradigm.