Interesting
Couple of thoughts, Haze can be yeast haze as in Hefeweizen, or it can be hop oils in massively late hopped beers, Glucan haze from things like flaked grain, Protein haze. Not all haze is yeast so it would be good to look at the style of beer you are making.
Long very cold Lagering, especially if you use good quality appropriate fining agents would I suspect do more good than trying to "de-activate" the yeast ( I would look at Isinglass and/or Silica xerogel). Fair chance that when the beer goes into the stomach... the change in pH and concentration would allow any surviving yeast to re-activate.
Along with Lagering, your yeast choices could play a role, choose highly flocculant yeast look at say US-05 and S-04, the S-04 drops like a rock when its finished and leaves way lower cell counts in the finished, with Lagering and fining this should be close to zero.
There are also some fairly affordable filtration options, I know you said you wanted to avoid heavy filtration, but a sterile paper plate and frame filter like those sold to home wine makers might be worth a look, especially if the beer is well clarified first.
I can do keg to keg filtration down to sterile (lots of grades of paper to choose from), just set it up and walk away for a couple of hours.
Mind you very little yeast should make it to the intestines alive, not a medical diagnosis (not qualified) but there is a fair chance that he is having a reaction to Gluten rather than yeast. He might be well advised to see is doctor and have that conversation.
Good Luck, Mark