you guys are funny.

ok heres my two cents., and then some,
first make SURE he can put the money where his mouth is... don't want to schmuck up your car and actaully do it then find out your buddy was just being a dick...
second.well yeah do a few practice runs when no ones coming or something. get someone to watch from the other side etc.
and just so that you can get a sense of what stock cars do...

i've got a 93 civic sedan and i'm an easy going driver but i like to have some fun some times. so i took a right turn corner on a block ripping at 70 Kmh and downshifting into second- note KMH. so for you that would be like 50 miles or something and i had on stock 2000 sir tires and rims and i slid / squealed out onto the oncoming lane and had to correct my wide turn as i faced oncoming traffic. SO, in my humble visions in my head, i can see someone doing this at 80 miles ( 100 kmh )and taking two corners, (right then left) and schmucking more than 2k of damage on it with a few cuts and broken bones.

i'm guessing even though without a picture, this S turn is NOT easy, considering youre friend is willing to bet 2k on it (not like 200). and even more, its on a highway so not are you endangering your life but you might be doing some damage to other cars. and you'll be DAMNed if you try this stunt at 3 in the morning with no cars cause you can't judge where anything is in the dark.

so i'd say do what FTB said and recalibrate your speedo