How does one book an AY-ticketed xONEx fare, originating in a city which AY doesn't fly/codeshare from?

Is there a central AY RTW desk in Finland, or can local AY offices in London etc. deal with RTW bookings?

(I've previously booked an AY RTW online, but that was ex-HEL and the tool worked fine, but it can't manage it if the first segment is on a different airline)