just get another 18" alloy of any style (but in escos fitment of course!!)

buy one off e-bay... there are always single wheels or part sets from crash damaged cars

put it in the boot where the spare goes , then jus get a vinyl cover made up so the wheel aint visible anyway!!

that should serve the purpose , jus remember not to get rid of the original tho as when ya come to sell the vehicle (if you ever sell the vehicle) the more gen parts ya have the better , obviously!!