I would not even "try" using the stock spare if you have 285's on your VX. I have 285's and I'm no auto mechanic but the variance in tire size alone would more than likely make steering extremely hard and may cause loss of control on road aside from your TOD malfunctioning.
Best bet I would think is to buy another tire like the 285's you have, get maybe a used 18' OEM Isuzu wheel, if that's what you have all around, and put them together. Good to have, only problem is paying for it and where to keep it....in your VX or at home.