Like pasta, Israeli or pearl couscous will absorb a lot of sauce. To get it creamy again, you need to "loosen" the sauce. It's easiest to do it in the microwave. Just reheat your leftovers for one minute, stir and add a tablespoon of water and reheat for one more minute, add more water if needed, and reheat until hot. The key is to stir once ever minute to prevent the sauce from seizing, and add in more moisture to get the sauce creamy again.