I used wobble bolts on my seicento when I ran 4x100 wheels. I'm now back on standard wheels so I have a full set of the wobble bolts, PM me if you want them
The problem with adaptors is that they tend to be very thick, and will probably push the new wheels out too far unless they have a massive offset. Wobble bolts (despite the name) are perfectly safe and the ideal solution for such a small variance.
ALSO bare in mind that the centre bore on non 4x98 wheels is usually different so if there specific vw wheels with a 57.1 bore they wont fit unless the centre is bored out . but a lot of the aftermarket wheels use rings to fit other cars . depends on what the wheels are to whether they will fit directly to the fiat hub or will need rings .