I'm not sure you'll be able to do that. Could you possibly pay for another TS & save the credit so that you have enough credits for the 2TS meal?
Our situation was a little more complicated - we had 3 people with a split room reservation & had 3 TS credits on one card (not yet expired) & wanted to use 3 from our new card for a Signature meal. At Coral Reef we were not allowed to do that. They had us pay for one meal with 2 credits from the first card, but we had to put the other 2 meals on the room key & have the resort take care of it. It did work out in the end, but it was complicated (and embarassing at the restaurant).