Blue smoke means oil. There are a bunch of different places it can come from. On an N/A car, the rings would be the first suspect, but on a turbo car, it would be the turbo oil seals. The turbo is located downstream of the engine, so if there is some oil, it would get burnt up by the heat, and come out the back end. Also, I believe if it is the rings, it would still do it when not boosting, where as this car only smokes under boost conditions.