Ilann
You‘d actually need a 5-zone extension ticket. But for whatever reason, in the Libero fare network (e.g. as opposed to the ZVV network), such extension tickets appear to be only available as single journey tickets, but not as return tickets (day pass).
So I fear you have either to bite the bullet and buy the regular day pass including zone 115, or then buy two single journey 5-zone extension tickets for 6.60 each.
