Buick Riviera 1997 Radio

[riviera]

Dear Buick-fans and -friends!
I'm new to this forum and live in Switzerland! Last year I had the opportunity to buy a 1997 Buick Riviera! They are pretty rare here in Switzerland!!
I like this car a lot, it's just great!
There is only one problem. Since this car was directly imported from the US the Radiofrequencies can only be tuned in 300khz steps, e.g. 100.3 MHZ, 100.6MHZ, 100.9MHZ and so on. But here in Switzerland the most Radiostations are on other frequencies.
Does anybody know if there is a way to toggle a switch or change something, so that my Radio can be tuned on 100khz steps?

Thanks in advance, Maurice