LOL, sorry for laughing, but I find it kind of funny. I was going to suggest cueing the sneeze to mean a treat too. Surely you can fake a sneeze for training purposes?
But I do have another idea. Just how much sneezing is going on, anyway? I've noticed for myself that the fan coming on, whether for heat or AC, often makes me sneeze. I theorize it blows dust out of the vents or disturbs dust in the house and that dust gets into my nose and makes me sneeze. So perhaps a vent cleaning and more frequent vacuuming might help limit the human sneezing?