I've flown UA fares in the that allow a routing like EWR-SFO-HKG-BKK with BKK-HKG on CX or HX. Does anyone know of similarly permissive routing rules (on reasonably priced W fares, I know that I can do almost anything I want to with a Y fare) that include SFO-SIN? I haven't had any luck finding them from a few cities that I've spot-checked on ITA, but I'm curious if anyone else has had luck, or if the best bet is leaving ample connection time and buying a separate ticket for onward travel.

Thanks!