I just purchased 4 used 4wd rims to put on my 2wd 2dr blazer base model, only to find that they obviously won't fit. Is there such a thing as an extender that would allow me to mount these rims on my truck? The local tire place said there's some kind of disk that can be bolted on to the existing posts and then it gives you 5 new posts to mount the rim onto, but he said they don't stay on well, anybody heard of anything like this?