Originally Posted by MZRIS
you cant backsweeten with fermentable sugars
Yes you can, I do it all the time. Like others said before me, use 2 plastic pop bottles. Fill one at the beginning, and one near the end. As they get firmer, you will be able to tell when it is time to pasteurize.
Also, keep your bottles in a cooler area as they carb up. 60 degrees will give you more time than 80.