Can I extend the pass?

Hi there,

I will arrive Tokyo on 14/04 and I plan to travel around northern area such as Fukushima, Sendai, Akita and Aomori. I plan to visit Aomori area for 19/04's cherry blossom festival, then come back to Tokyo maybe on 20/04 or 21/04. This means I will need a 7 or 8 days pass for East-South Hokkaido rail pass. However, I can only find a 6 days one. Is there a way to extend 1 or 2 more days on the pass? Or what would be the best way in this situation?

Thank you!