i have seen it done on some 911 race cars
Yup, I've just recently sold a set, they were 15x6 banded to 15x8. But the Fuch alloy wheel design lends itself to this and they're high quality forged items to start with so stand a bit of welding.
Also if you watch American Hotrod from time to time they have a machine that does it. A bit like a tyre fitting machine that rotates the wheel and the welding tip is secured at a fixed point and welds as the wheel turns.