I think the problem that you might encounter is that the fondant must adhere to the frosting. Fondant is usually applied directly over fresh icing, so that it doesn't fall off, and if you pick up cupcakes that are pre-frosted, the frosting might already have hardened a little.
You can make a disc of fondant, write the words on it, and then put a dot of fresh frosting on the cupcake and then stick the disc to the top of the cupcake. It can be done in advance. Maybe the Sam's Club bakery can supply you with a little bag of extra frosting for that purpose. You should probably inform the bakery that you plan to add a fondant disc to the top so they don't make a giant swirled bunch of frosting on the cupcakes, like the soft-serve ice cream in a cone.
But I have another idea. (Diane B, I believe she's referring to the Alice in Wonderland original book, where Alice finds small cakes with the words "eat me" written on them. The cast members, if they're in a play, will easily identify the reference of the words.)
In the book, the words are written in currants. It would be pretty easy to ask Sam's Club to make the frosting on the top of the cupcakes fairly flat, not a high swirl of frosting. Then you could cut up currants or dried cranberries or golden raisins and form the words "eat me" with them, by sticking the fruits into the frosting and using a toothpick to nudge the fruits into place.. It might be easier than cutting fondant circles and writing on them, and it's truer to the book. Just an idea.