We are waiting Adobe Muse letting us any way to add user chosen number of fields in widget settings. We hope we can do it soon, that would avoid a lot of headaches.
Anyway, since that is not so big requirement and we just launched our support forum, maybe we can make an exception 😉
It would be enough 16 options just on first attribute group? or do you need 16 in each one? Are you using widget with or without leading zeros?