If the wheels really are the offset they claim to be, and these aren't some chinese replicas or something where they claim ET51 but they're not, then you already have wheels which would clear a "regular Golf". Maybe what you should be doing is taking off the wheel in question, taking a photo of your wheel arch with the fuel tank pipe you mention in the 1st post, and showing that to us so we can have a look to see whether it's the same in our cars. There aren't many Golf 77TSI peoples around here... even less who go and change wheels etc.

The other question is what tyre size where you thinking of putting on?