Crazy idea but... what if you went veggie for a week or two? I mean if he's eating them hidden it's obviously not a taste thing. You could do things like crudites and dips for lunch (Stan won't eat many raw veggies plain but will if he can dip them), or a lovely courgette soup, pureed smooth with some cheese grated in (much more popular here if he can drink it from a cup - novelty factor). Veggie risotto or veggie curry for tea, something with all the bits cut up really small and mixed well together so there's less scope for picking bits out. If he doesn't eat it - no fuss, no pressure, just try again tomorrow.