Europe / Schengen Visa Extension – in Greece ?

[Burls]

We’re Australians presently cruising Europe, and are rapidly approaching our ‘maximum 90 out of 180 days’ stay within Schengen Countries. Our research so far indicates that you are not normally permitted to extend your stay in Schengen countries, however, there have also been examples where people have negotiated extensions on a case by case basis, in various countries. (One example post on this subject is: http://www.cruisersforum.com/forums/f57/visa-issues-in-schengen-countries-32067-2.html )
We were just curious if there is anybody out there who has actually successfully extended their Schengen stay beyond the 90 days, while in Greece? If so, any information on how you achieved this, and how long it took, would be much appreciated.
We’ve heard that you can go to a Police station or ‘Alien centre’ if there’s one in that town, to request such an extension?
If the wheels fall off, then it’s off to Turkey, but we would like to spend some time in Greece if we can make it happen.

Thanks!

Burls