Teaching a boy to hold his penis while he pees

My son is 3yo, he's figured out that boys can stand while they pee and does really well so far. No wildly crazy aiming or trying to pull tricks like peeing as close to the rim as possible.However, I can't get him to hold his penis while he pees. He sidles up to the toilet, drops his drawers, assumes the position and just flops out his penis then starts going. At home it's not a huge problem our home toilets are shorter than most of the public ones we've encountered and family germs dont give me the heebiejeebies as much as stranger germs. In public restrooms though, the rim comes up so high I'm always hovering and trying to hold his penis up so it doesn't touch anything.Parents who have had this issue, how did you teach your sons that they needed to hold on to their penis while going? Just keep repeating, you've got to hold your penis buddy? Is this a guy conversation that dad should be in charge of? There's no going back to sitting now, he even gets a little frustrated when he sits down to poop and pee comes out ("We stand to pee and sit to poop mommy!"). Help! via /r/Parenting http://bit.ly/2KsaVBs