When I first saw the rear mount idea I initally thought of all the problems that you say, however, in the states this is a common mod and all the issues have been resolved.
In fact when you start thinking about it in detail , most aren't actually problems. the puddle one potentially is, but the turbo will be running much cooler at the back.
As I think I may have said, ther rear turbo idea is used in the states to get around a law that restricts you modding the exhaust manifold (or something like that). If you don't have this restriction , then sticking the turbo close to the engine is the best idea. The rer mount is doable, but it's a compromised design with no benefit.
There is a law in the US that restricts the modification of factory installed Catalytic converters on exhaust systems. You can get an after market high flow replacement unit, but still need to run one if the car was so equipped from the factory. The rear mounted turbo allows for a mounting after the Cat and in many cases won't void a factory warranty on the un-modified part of the engine and exhaust. Of course this does not apply to Minis here in the US.
