I especially liked Sham
There is however one person in the Fellowship who might have known a way - Aragorn. He himself went on the Morgul road, and he had been on journeys very far away, even all the way South to Harad, "where the stars are strange". Clearly it was far away,since he seems to have passed in the Southern Hemisphere. If he had traveled so far it might be that he had discovered some other way to enter Mordor, either from North Ithilien, South Ithilien or from South of the Mountains. Of course all this is speculation, but it would make sense.