I'm not sure how fuel would make any difference since it's not going past the valves. As far as I understand, the use of two oil catch cans is the way forward, and BMW dealerships may be investing in walnut blasting machines to loosen and remove the coking.
Its the consequence of burning normal fuel, and not a lot of use.
From I have seen on the internet there's a lot of stupid Americans running them on the cheapest fuel available, and they are the ones with the most problems.