You could last year. We were on the Dining Plan and booked the Candlelight Processional. It was not a problem at all. Just tell them when you call (which I'd do asap if I were you) that you want the CP dinner package and you're on the dining plan.
There are a limited number of seating for the CP dinner package and you the coordinate the dining time with the CP package. If I remember correctly, we had a 5:10 dinner and the late performance of the CP (8:00?).