tuff wheel adapter/extension?

i just installed my grant repop tuff wheel (http://www.grantproducts.com/products/view/88/). i have a nice little gap because the cap? or what ever on the back of the wheel doesnt match up to the column



what do i do to fix this?? is there some adapter i can get that tapers or covers the gap? the wheel also seems awfully close to the column, so i was hoping there would the an adapter than would fit between the wheel and the column an push the wheel out towards the driver like 2" or so?

thanks and if you have links, id greatly appreciate it!