Reply #3: There are two approaches:

[Lydia Leftcoast]

When I was a Lutheran, where the grape beverage is served in individual little cups, it was an open secret that the cups on the innermost ring of the cup holder were grape juice.

In the Episcopal church, where the common cup is standard, it's difficult to offer that option. In that case, people take the bread and then cross their arms over their chest to indicate that they won't be receiving the cup.