Chris -
Although I usually mount mine up in my roof rack (a little different than Josh and Brian), I have also secured it at times in the back of my Sport.
With the jack in the vinyl cover, I just cinch down two friction straps on the rear-most "C" hooks (the ones for the net).
There is just enough room for the jack to lay flat along the width of the hatch area. This works in my '91, not sure if it'll work in your late model Sport (especially with your interior tire mount).
Paul
'91 Sport