You talking about the pin inside the throttle housing on the end of the handle bar? You can either drill a hole and glue a part of a bolt into it to provide the location. Or, you can put a sheet metal screw thru it to locate it. Or, you could buy a new one and replace it.
Had the same problem. Just wrap the clip on in a few turns of electrical tape and tighten the housing on to the tape. Be careful you position the tape so the throttle tube has no chance of getting stuck on it though.