But you really think it's so unlikely that someone picks up this knowledge without a degree? The textbooks used in universities are available to the general public, and there are also resources like Coursera that do provide a semi-traditional learning environment without conferring a diploma.
Unless you're really drowning in candidates, it probably makes more sense to interview for knowledge of CS theory (or use a standardized test) instead of doing a resume-filter.
Your anecdotal evidence is easily countered by other peoples' anecdotal evidence. Mine, for example.