X.O.
Haha, just yesterday my oldest picked his nose and ate it. I told him it was disgusting and he said, "No, it's not disgusting, it just LOOKS disgusting." Do you know what? He's actually right. It is gross to look at, and can cause nosebleeds, but other than that, it is not really a health hazard--just not socially acceptable.
But, perhaps get him some Boogie Wipes, which are saline-soaked wipes that can help loosen the boogers so he can clean them out without going knuckle-deep :)