I am trying to book the above using UA non-stops from SFO-NRT and CDG to SFO, with a star carrier like Asiana for Tokyo-CDG..but can't figure out how.

United will only put me on NRT-SFO-CDG connection which is 24 hours long. If I book the SFO-NRT and CDG-SFO as one ways and buy an Asiana Tokyo -CDG myself, the SFO-CDG UA segments prices at $4,000 just by itself.

Tried StarA around the world, said this was not valid routing. I know somebody here can help me!! What'st he best way? I will be in Y....