It's been a while, so just an update! His toe-tapping has stopped as we're still doing the elimination diet. At this point, it's likely cantaloupe/rock melon (I just realised I had completely forgotten the name cantaloupe and was accidentally calling it honeydew instead - been away from the US too long!) or starfruit.
He does get tiny almond chips (we break up almond slices into small pieces, almost watermelon seed size, to avoid fatty liver issues) as treats. He had been doing quite a bit of training, but luckily, no toe-tapping. I'm just trying to make sure we also balance his treat eating with enough exercise.
His digestive problems seem gone completely

Now it's just the time-consuming trial and error with food. But I'm glad he's healthy. Hopefully in a week or two, a blood test will give us a good baseline!