paid subscriptions over fixed periods

[Barteh]

I run a clan forum and we're using the vB paid subscriptions manager to deal with clan subs.
The issue we're having with this however, is that rather than a fixed expiration date this only allows extending the current subscription time period. This means that, for example, new members paying their subs after our yearly renewal date, would suddenly run out mid season. Or the other way around, members paying early when the right payment amount hasn't been calculated yet.

Is there any way to make the all subscriptions in that one group run out simultaneously (on a date set by the clan treasurer), other than mass editing individual subs?