I would think a post on either side of the driveway entrance with a chain hanging betweeen them would do the trick at a relatively low cost. The downside is you’d have to take it down and put it back up each time you wanted to come or go. The upside is that you could lock it which would pretty effectively block him from doing what he’s doing and creating your problem.
This is a good idea but I have a neighbor who lives downstairs who probably wouldn't like that idea.
Now I'm thinking that maybe all I need is to think up a reason for a sign to be staked in the dirt spot so he'd have to run it over or turn right. Not a "don't turn left" sign, but an ad of some sort. There's a pseudo-church up the alley, so I could put up a sign advertising an upcoming Holocaust survivor's speech at a different local church. That doesn't appear antagonistic, and people should go.