Right, since I've just had to take my crank arm off which was similar to this, I'll explain in what i did. Firstly I flooded the area on the bolts and around with wd40 and left it for a couple of hours. Then, when i came back, i superglued my allen key into the bolt and stuck a big pole on the end of the allen key. Make sure you get someone to hold the frame though! Not sure how much of your bolt is rounded though.. If superglue fails, loc-tite it in. Anyway, give that a go. Good luck, Joe