Okay, I'll add my two cents.
Yes, if YOU are the one that caught him, then YOU need to be the one to discuss it with him. To have dad or an uncle or other "father figure" talk to him only says "OMG! SHE TOLD EVERYBODY!" and no discussion will be productive at that point. When you do talk to him about it keep it simple and to the point. "Hey, it's natural but keep it private. If you have any questions..." yada yada yada. You, know the drill.
Oh, and as far as the use of a hot dog bun goes...
well...
it's not that big of a leap if you think about it. So, I wouldn't even mention it.