I'd suggest both answers lie in getting a welder and doing a bit of fabrication....
I'm not sure how much extra height would be required in the wheel carrier for a 31" tyre to clear the rear bumper; there's about an inch of space between the 235/70/R15 on an 15x8 rim (don't ask) and the bumper itself, so I'd be figuring at least 2-3" higher. It wouldn't be hard to make an adapter from a bit of 6mm plate and welded on 3 bolts with the correct PCD positions. The adapter itself could bolt on the existing 3 wheel bolts, or you could just weld it on.
All that said... I'd be a little worried about the rear door's ability to handle the extra weight though. Personally I was counting on fitting up a swinging rear wheel carrier to take the spare when I move up to bigger tyres.
As for the front bar, so long as your Zook doesn't have airbags, anything can be fabricated up to suit.
Cheers, Ben.
