The best thing you can do is to explain the situation to the priest. Let him know that not only will non-Catholics be in attendance, but also that some of them reject the Church’s belief as to who can receive. I wouldn’t suggest putting it in the program, because people either won’t read it, or will ignore it. Let the priest handle making an announcement at some appropriate time. If people hear it from the priest himself, they will be less likely to ignore it. In other words they might think “not only is it in the program, but the priest means it when he says it.” Doing it this way also “insulates” you in a certain way from criticism. Those who have a problem with it can complain to the priest who made the announcement, rather than to you who put it in the program.
Bring it up to the priest, but let him handle it. He’ll know what to do, and how to do it.