Without looking at the disk, it seems entierly possible it WAS a synth, with Jan Hammer playing it. He has always soundsed very guitar like in his phrasing, and he was all over that record.
I think Beck plays through a ring modulator on "Sophie" if I remember correctly... let's see... naaaaaa, it's too buried in the disorganized pile that my CD collection has devolved into for me to go dig out and play now to check, but I think I'm correct...