Most "KC style" pulled pork I have had doesn't have finishing sauce on it. They either leave it as is or put some BBQ sauce on it. If you want to use BBQ sauce thinned, I would possibly use some apple juice. Haven't cut sauce with apple juice before, so just a suggestion. I personally would use a vinegar based finishing sauce myself. I have not read KCBS rules, so I don't know if they would ding you on it. I thought they went for taste, presentation, etc..... not necessarily true KC style. Heck I was even told they don't judge on smoke ring anymore, because you can put certain chemicals on your meat and it gives it a "smoke ring" look even if it were cooked in the oven. Now I am sure off the record they are looking at the smoke ring though, and I bet it still plays a factor visually if nothing else.