One of the bolt from the cam gear got cut in half,

You probably can't. They are "Sweat fitted" when they are made. The cam is heated and put into it's EXACT position, onto a cold shaft. When the cam cools, it is locked into place. If you try to move it by heating it, you will be heating the shaft too. You will also be changing the hardness of the metal. Bad news is--you need to buy another cam shaft.