This has been done before... Jeff Gordon and Juan Pablo Montoya did something like this at Indianapolis some years back...

Barring an unforeseen scheduling hiccup, two-time NASCAR champion Tony Stewart and 2008 Formula 1 World Champion Lewis Hamilton will swap racecars in an exhibition later this year, Stewart-Haas Racing spokesman Mike Arning confirmed Saturday. The seat swap comes at the hands of Mobil 1, a mutual sponsor for the two drivers, and is expected to take place at Watkins Glen International sometime during the summer. The cars involved will not be show cars. They will be legitimate race-prepared machines. Hamilton will man Stewart's road course ready # 14 Chevy, and Stewart will drive Hamilton's 2010-model F1 McClaren. The respective drivers' race teams will travel with them to the event to tune the cars.(ESPN.com)(2-27-2011)