The best way to show that Aristotle's physics and metaphysics (not the books, the subject matter) are isolable would be simply to note that the latter doesn't require the former - it is not a logical requirement to hold (the relevant) Aristotelian metaphysical positions that one holds Aristote's views on physics, nor is it the case that there can be no good reasons to accept the former if one did not accept the latter. At the very least, a detailed explanation is required to show why they are not isolable, which is unlikely to be given (not least because the sort of people who make these objections tend to have next to no familiarity with even reasonable secondary sources on the issues, let alone the primary sources).