You could do what this GIANT Austrailian company did and charge an extra "tax" for old browsers in compensation for having to support them
'It appears you or your system administrator has been in a coma for over 5 years and you are still using IE7.' It begins, before going on to break the news about the costs. 'To help make the internet a better place, you will be charged a 6.8% tax on your purchase from Kogan.com.'
