big fan of the 'do the advert, take the money, slag it off afterwards' approach as yer man has done a great example of here:
http://pitchfork.com/news/60297-justin-vernon-says-there-are-no-plans-for-another-bon-iver-album-or-tour/

Trent Reznor is great at this as well 'turns out that doing a song for the Tomb Raider soundtrack wasn't the best idea'

What else works?