Toddler can hold pee but has difficulty releasing it

We're in middle of training our almost 3 year old who has sensory processing disorder. He caught on to pooping fairly quickly (he always hated the feeling of dirty diapers) and is learning how to catch it before it's too late.

But he's totally lost with peeing. He has great bladder control & will hold his pee for hours at a shot (even with tons of liquid) but he seems lost for how to release it intentionally. Having him sit on the toilet is useless because he won't pee when he's focused on trying to pee. It only comes out as soon as he is 100% distracted & relaxed with his favorite toy. We've tried making the bathroom more "relaxing" (playing music, games, books) but nothing helps.

We only had success on one day when we caught him mid-accident & he was able to finish the pee in the toilet, and he was able to pee voluntarily multiple times later in the day that same day. It was a lightbulb moment which lasted the rest of the day ("oh, THIS is what you want me to do? Sure, i can do that"). But the next morning he had forgotten how to do it, and we were back to square one...

Catching him mid-accident is super hard because he holds it in for so many hours. Impossible to predict when that accident will finally happen....

Is this an age thing? Or is this expected? Right now we're fully commando. Tried bare-bottom but my son couldn't tolderate it due his sensory challenges, so commando is the only option for us at the moment. Feels like we just need to repeat that "catching mid-accident" a few more times & he'll get the hang of it, but I don't know how we possibly can catch those accidents, especially commando.

Any ideas or advice welcome! We're thinking about waiting until he's a drop older (and hopefully more body aware of his pee) but he was doing so well with pooping that it's a shame to stop...