I'm well aware that I am the only person interested in this thread. But I can't resist posting the latest two answers, received by email from CBSA (the second one, by the way, THREE MONTHS after I sent my question). Again, the real point is that this just doesn't seem right.
Answer 6: There is no provision in legislation for relief of duties, so these must be paid (to which I replied by referring to the publication so helpfully provided by yyzvoyageur, which prompted:
Answer 7: There is no duty on laptops imported permanently to Canada, but you do need to declare and pay PST/GST.