I had the exact same problem several years ago, and the bolt was pretty well rounded off. I took it to several oil change places in my area, however they all said they couldn't get it off and I was in trouble. I took it to the dealer, and they got it off and put a new one on for me. Charged me like 5 bucks for the bolt, but hey it was worth it. So my advice is to take it to the dealer, they will get it done for you. Than begin changing it yourself next oil change.
