maz I have worked with a few spectrum bunnies, and I have seen this SO MUCH. Have also seen it in other kids but the reaction doesn't seem to be as intense. If you think about it, when you've got a *ahem* "turtle poking its head out"... it's a very distinct physical feeling, and I guess you can understand why that's just one more thing he has to process, and hence starts to wig out.

Can you sneak some psyllium husk in with his milo? Or somehow get it into him before bed the night before? Definitely will nto hurt him to up his natural fibre intake, and good thinking on the banana.