From comments on the blog post:
1) stonefamilytree offered: "Try using the descendant list on WikiTree to see who else has linked to your ancestors, and then contact those profile managers."
2) Geolover suggested: "An offshoot of your No. 1 -- has there been someone with contact information currently making entries who can be contacted via individuals' "Latest Changes" sections on their individual pages?"
3) Keith Riggle listed: "You've hit the major ones but here are a few more:
1. Facebook family and locality groups
2. Surname forums and listservs
3. Lots of lesser know family tree sites like Tribal Pages (hit & miss like Ancestry et al.)
6. Newspaper obituaries often list surviving family members