Wow. I tried to force one of my Nokians into the spare tire well of my Golf before it was mounted on a wheel. I may have been able to do it, had I really tried, but I was concerned about it getting stuck in there.
I ended up filling my spare tire well with one of the large foam inserts from the 20th Anniversary GTIs (which had no spare tire). It has space for the jack and other tools, a bottle of sealant and the factory portable air compressor. The insert supports the floor, so I can keep my full size spare in the "trunk" area of my Golf. Having the spare there isn't an issue 99% of the time. Now that my kids are teenagers, we usually take our minivan on long trips. The wife and I still take my TDI on road trips when it's just the two of us, but then we can use the back seat for cargo.