How to set Paypal button with a fixed target expiration date

I am setting up a membership site with an opening special - A one-time prepayment for membership through Dec 31, 2012. This is a significant discount over the monthly payment option.
I have set up my Paypal button for the monthly payment option.
Is there a way to create a Paypal button for the prepayment option? The price would be the same, whether someone signs up next week or 3 months from now. But all such subscriptions will expire on Dec 31, 2012.
If this is possible, I'll need to send out a notification in Nov 2012 to all prepayment subscribers, to renew at the 2013 rate in January 2013. Is there an automated way to do this?
Thanks.
Pauline
I have set up my Paypal button for the monthly payment option.
Is there a way to create a Paypal button for the prepayment option? The price would be the same, whether someone signs up next week or 3 months from now. But all such subscriptions will expire on Dec 31, 2012.
If this is possible, I'll need to send out a notification in Nov 2012 to all prepayment subscribers, to renew at the 2013 rate in January 2013. Is there an automated way to do this?
Thanks.
Pauline