Hi Tree, I lost my bunny to stasis last year (long story, see Tufty for details) and whenever I read about this topic, I always feel I have to share what I know. Millie was prone to bloat and stasis, despite being on the exact same diet, regime etc as my other five. Like you, I follow an emergency plan whenever I see the first symptoms of stasis, and usually this worked with Millie, but her last attack was very severe and started through the night so I didn't catch her early enough. She ended up having two trips to the vet, for fluids and metaclopramide, but then ended up at the emergency vets who operated. I was devastated when she died.
So, the lesson learned - she was found to have septacemia when they opened her up, which (having talked with my usual vet) may have been because her tummy burst. It was suggested to me that Millie may have had some sort of inflammation, or an ulcer, which was aggravating her tummy now and again, thus causing stasis and bloat. I was gutted to find out that had this been diagnosed earlier (perhaps thorugh an x-ray as you had for your boy) then she could have been treated with Zantac syrup rather than metaclop. Maybe this still wouldn't have save dher but it would have been nice to be able to try. Zantac apparently has a similar effect to metaclop, although acts in a different way, and would have helped her had she had an ulcer/inflammation. Reuben, one of my gang, has taken over where Millie left off, and has had about 4 attacks in the last 6 months - he, however, has been treated with Zantac and recovers well. Since his last course, he hasn't had an attack.
I know there are lots of diet-related discussions going along with stasis and bloat, but if you're at a loss at to what it might be because you've excluded everything that could cause bloat (broccoli, sugary fruits, kale etc), you've cut down significantly on pellets, they eat tonnes of hay (readigrass type grass can be a bit bloaty too apparently) etc, then I'd ask about Zantac syrup - its worth a try. If your vet wants to contact my vet then I'm sure she'd be fine with it. Judith Brown at First Vets 0191 2666286. Hope this helps...