reset sqlcounter on the same day for each user

Hello everyone. Need some help. I want to limit my users with MB traffic monthly. I have set up sqlcounter and it works great. But it resets in month starting user first connect to NAS. Users can register and connect on different day during the month and then it resets differently for each user. And this is the question. How can i reset counter on the certain day for certain user(example last day of month).And then counter can resets monthly for all users beginning from the first day of month. Maybe I need some attributes or ... Thanks