How to extend a paid period manually?

I often offer a couple of months of the membership as prizes for various activities, contests and promotions. Normally, if someone is on a monthly plan, I will just pause the membership for the period they won. How would I do that if someone is on an annual plan? If I pause it on Paypal will it actually postpone the next renewal? If so, great. If not, what would be the best way to go about it?