I'd mention the obvious and say that he should be more understanding and you shouldn't have to worry about feeling judged, but again, I guess that's obvious. :P

Would you be up to going to the beach with him, maybe even just relaxing while he swims if you aren't up to swimming?
Is there any sort of project or thing you've been wanting to work on, where maybe you could use his visit as motivation but still be kind of doing it for yourself, too? I'd suggest the library for books, but I'm guessing transportation would be an issue.
You could also look up documentaries or something online and spend some time watching a few. I like to do that when I'm trying to be just a teeny bit productive, and tell myself it's better than TV because at least it's educational. :P