This is a bizarre story. He is indeed lucky this didn't happen in Singapore, or any Muslim country for that matter. He wouldn't be spanked either. A caning, public or otherwise, in such a place is no trivial matter. Public humiliation would be the least of his worries.
Yes, he should be "dressed" in some type of garment that would cover him in front but leave his backside bare for his punishment (not unlike a "Spank Shop" apron from one of Seegee's stories) and he should be spanked over the knee of a capable female spanker, like a naughty child, very, very, thoroughly with at least a hairbrush or paddle until he literally can't sit for a week afterwards and he is sobbing incoherently in compete submission. Perhaps a few strokes from a leather strap or tawse as well and then posed bare-bottomed for all to see. "Pranking" is one thing, but this is sexual assault. Maybe this will cure him of his desire for attention. I'll bet he'd get plenty of attention afterwards...