Well, after a year of aging, the yeast have most likely all settled out. So I don't know if you would have any viable yeast for CO2 production, even by pulling some of the lees off the bottom of your carboy. You might have to add some fresh yeast, along with your sugar in order to get it to carbonate. With 2 gallons you would probably only need about 1/4 to 1/3 cup of sugar, along with some fresh active yeast.
Primaries - all empty
Secondary - Several Hard Ciders
Bulk Aging - Brewtopia Barleywine