Make him find 20 married women and tell them he doesn't play away from home, but wouldn't mind if they did......
Other options
Fine him booze at every turn for breaking tour rules that have been made up in the spot - for wearing a blue shirt, for not wearing a blue shirt....
Make him carry around a cuddly toy (like Itoje's about to ).
Set him a challenge like acquiring a sign post, preferably one set in concrete. (c) Dublin 1995.
Nick his jeans and run them up the hotel flag pole. Dublin again!
My favorite was the Bath trip where one of the guys failed to mention that his 40th birthday fell on tour. Heinous in the extreme, but nothing a quick stop at a charity shop and an over sized judo suit that he had to wear for the rest of the trip couldn't sort out.