How much sugar to bottle for this

So I'm about to bottle a batch of pumpkin chai beer I got the recipe here

http://hopville.com/recipe/108036/american-brown-ale-recipes/pumpkin-chai-ale

In the recipe it says to add 4 cups of chai coffee made from simmering two cans of pumpkin at bottling

Since it's a 3 gallon batch I would normally just add about 2oz of corn sugar, but how would I figure out how much sugar the pumpkin adds? Or it is not enough to be concerned about? I had my first bottle bomb with my last pumpkin batch I'd (and my girlfriend) would not like to repeat.

This is something that has gone through fermentation and has finished?

A tad less than 2 oz for 3 gallons sounds right.

It's hard to calc a final gravity because of the adjunct (pumpkin)

My pumpkin beer finished fairly low.