Regular, Premium, Carbon Neutral?

While Terrapass and others offer carbon offsetting for the CO2 that your driving emits, I wish gas stations would start offering it at the pump. Instead of having to figure out much I emit for an entire year and then purchase a year long pass from a website, it would be so much easier to pay for it with each gallon I purchase.

Terrapass sells carbon offsets for $.10 a gallon (6,000 lbs of CO2 for $30 = $.005 per lb * 20 lbs of CO2/gallon). For an extra $.10 I could offset the carbon my gallon of gasoline causes. At $3.00 a gallon, what is an extra $.10? If it was as simple as pressing a button when selecting the grade of gasoline you are buying, that would be great. Well worth it for the peace of mind (and smugness) it allows.

Seems like some gas station would offer this as a way to draw in the Prius driving Whole Foods shopping crowd, plus as a way to generate more revenue (if they wanted to take a $.01 cut on the whole thing, sounds fair to me). Wonder how long until someone offers it?