[Koha] irregular serial numbering

Hi, I'm having trouble in defining the numbering pattern for a serial. The serial is weekly (number icreases by one every new week, and is never reset to one), but the volume number increases at the beginning of each new second month. This means every 7, or 8, or 9 weeks (i.e., issues), depending on whether the two months contained 7, 8 or 9 weeks. Would it be possible to define such a numbering pattern with Koha? (FYI, the serial is "Nature".) Many thanks and best regards, Giuseppe.