You could take the Narita Express to Shinjuku and change to Oedo line for 1 station to Tochomae. The Oedo fare should be about 160 yen and not covered by the Narita Express ticket.

As far as I know, all Narita express trains go to Shinjuku. The train decouples into two at Tokyo station where half go to Yokohama and half go to Shinjuku. On the timetable one train appears as two. Once at Shinjuku, some Narita Express trains go to Tachikawa/Hachioji on the Chuo tracks but while others go to Ikebukuro.