Points 1 - 3 suggest this opponent is simply a lot better than you at your current level.
1) by forcing myself to change direction, i introduce higher risk of errors.
Okay, this is a basic thing you can practice. Everyone practices playing 1 BH - 1 FH themselves, but you also should be able to play from one spot and move the ball between your opponent's FH - elbow - BH. Might as well practice in these matches since you don't take lessons with a coach, and are losing to this guy anyway. Make is useful and more interesting.
One thing to note, is he is a penhold player, so I don't think he has a elbow weakness like Shakehand players have. But I agree, since i'm losing the % game anyways, I might as well try out something different.
2) he might just block back to my BH, and i'm still stuck in the same position
This is an interesting answer because of what it shows about your tactical thinking. You are not in the same position at all. YOU are playing the same shot from the same place, true. But if you play back wide to his backhand, he now has to move to cover that. Does he still play an un-attackable, low, dead ball when he has to step to his left to get to it? Then he is a very good player.
I think when I tried changing directions on him, I wasn't really able to stretch him enough out of position. He just stands very close to the table, and can hit both forehand or backhand from the same foot position. Every ball that comes back to me is always the same, its low, its close to the table, its a little dead, and its right to my backhand corner. Again, I COULD try to hit wider and stretch him more, but this wouldn't really help me win more % points. It might win more flashy points, but my overall % would drop due to increased errors.
3) if he senses an opening, he might block cross court to my FH
This is actually kind of what you want? I mean, I'd be praying for this pattern so I could play my forehand down his backhand line. But even if you don't have a down the line forehand, getting your fh into play should be the goal in this situation. You are losing at BH - BH. FH against his middle might work out better.
So a drill that might be useful if you can find anyone to train with (and it's fun!) is the one where you play bh - bh and at random one player is allowed to redirect to the fh, then it goes free. There is a variation where either player can redirect, but that creates an incentive to be first so may not be as god in this case. Or if you don't have anyone to practice with, practice it in the matches with this guy. Sounds like he lets you be the one who can change the play to fh, if he will stay on bh 20 - 30 balls in a row.