Renault clio snapped bolt removal?

The easiest, most sure way to get this out would be by welding a nut onto the end of the bolt. This will do two things for you. First, it will give you something to turn with as when the nut is welded to the bolt, it will become just like it was (for the most part) when the original head of the bolt was present. Secondly, during the welding process, what is left of the bolt will expand greatly, which will break the bond between the bolt and the hole it's located in. If you weld it, then wait until it cools down a little, it should quite easily turn out of the hole. I can't tell what the hole material is made out of, however, it looks like aluminum. If this is so, it works especially well in these situations.

In trying to turn the extractor to remove the damaged bolt, you are applying torque to the extractor using a tool. The amount of torque you can apply is limited by your strength and the length of the tool's lever arm - that is, the distance between your hand on the tool and the axis of the bolt.

To increase torque, and hopefully remove the damaged bolt, make the lever arm longer. Use a different tool. Or extend the tool's lever arm by, for example, using a piece of metal pipe placed over the existing tool handle. If you double the length of the lever arm, you'll double the torque being applied to the extractor. Remember to wear eye protection.