Is it permissible to say "Ameen" to the supplication of a sheikh from a previously recorded tape?

Supplication (Du'a) and saying "Amin" to it are acts of worship. What is legislated is to say "Amin" to the supplication of a present supplicant. As for supplications recorded on tapes, it is not legislated to say "Amin" to them, because there is no one actually supplicating.