would be cool if you'd take a look at http://www.redballoondays.co.nz/category/Driving/motor-racing and let me know if any of those experiences look like a bit of fun? not sure which if any of them would be worth doing... the little F1 things look like they might be good fun, but i wouldnt know!
all of them would be pretty fun, just comes down to personal preference really. only caveat i would say that the single seater cars (f1 style) generally tend to be quite tight so if he's a big bloke that may be an issue to think about.