I don't think it'll work like that - each table service credit doesn't have a set value, so how much money would they apply toward your Signature meal?
Instead, you could possbly ration out your credits - maybe split a couple of table service meals earlier in the week, or have two counter service meals one day, or something like that. Trust me, you get a LOT of food. I came home with four desserts, two sandwiches, three bottles of water AND I gave away two fountain drinks to people in line ahead of me. I also ate (a real) breakfast for the first time in about six months.
