When offering on-the-spot products at events, only promote a few products.
You might try: taking a picture of someone at the event, or having someone send their pictures of themselves at the event, and then sublimating it onto a product.
You could even use a green screen to come up with a custom background for the event and then take pictures of people standing in front of it, then print it out and sublimate it.
-David Gross, Condé