two suggestions for you:
1) Hang a 500ml drinks bottle off your balls, and slide it down one leg of your trousers. Hopefully you have a pair of trousers that are loose enough there is room for it to dangle there and bounce around pulling on your nuts as you run
2) Give yourself an enema with 500ml of stale morning piss before starting off. Oh, and no pooping at all for two days beforehand. No diapers or anything, just dressed normally. Hopefully you can finish your run before you lose control of your cramping guts, cause that mess is gonna be nasty