To play Tokaido solo, I am using the Two Brothers solo variant that was posted here:
with one modification. I don't think this variable is actually winnable as presented, so I changed it (based on a later comment in the thread) so that only the first brother that arrives at the Inn scores the six points for the meal. The later brother will still get to eat a meal and keep it to try to score the Gourmet (or whatever it is called) Achievement, but he has to come down and eat his meal later when no one is around so he doesn't get the six points. If they both showed up in the dining room together, their gig would be up. That's my in-theme rationale.
Here's how things looked at the end of the trip:
Even with my modification, I still ended up losing 105 (55+50) to 80. But that was OK by me. This variant DID give me a reasonably interesting way to play Tokaido solo that felt like a multi-player game and I hadn't played Tokaido in a long time and certainly didn't play optimally. I misspent my money and couldn't afford a meal at the Inn once, for instance.
I think I'd play it again with the same scenario (or maybe make the trip back as the variant suggests when you lose on the way out) before I tried modifying it any more. I'm sure I could have played a lot better and made the score closer than it ended up.