How to make pre-placed glue sticky only when needed>?

If I had a product I wanted to market, where glue was needed to be used by the consumer and was pre-placed appropriately in the needed position, how would I? I cannot reveal the actual product for privacy and confidentiality reasons. But an example would be small toy baseball caps that could be permanently attached to a dolls head. How would you make it so that the glue is already on the appropriate place in the cap so the consumer does not need to apply the glue themselves, but still make the glue sticky at the appropriate time? It is essential that the glue be strong enough so that it sticks near permanently the surface it is being applied to. So an adhesive like those where you peel off the plastic and reveals a sticky surface (very weak glue) would not work.