Piggybacking off your suggestion, I like the idea of holding up a sign advertising a free activity that anyone can join, located in a very public space, with zero committment, so they can both show up and walk away at the drop of a hat. Whether it's an ad hoc organized chess tournament, or D&D game, or "one word story" or literally anything. That will have to wait until nicer weather, though, to avoid having to rent a place.
I feel the best way to do what you seem to want to do is by meeting people where they are. No matter what you do, the last part of your mission relies on the lonely person. They have to choose to connect to others and then they have to do it. Arguably, that's the hardest part.
Your instructions to comment on your blog are incredible, come talk to you face to face. If I didn't live on the other side of the country it would be meaningful to tell you what it meant to me in person.