Make sure you are using the most up to date version of the client (it should be called "Beamdog Client" and not "Beamdog Experience"). You should be able to play them without internet access. I just tried launching them from the exe from the folders and they worked.
Also the client itself has an offline mode (though having it active as far as I'm aware isn't necessary).
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Also the client itself has an offline mode (though having it active as far as I'm aware isn't necessary).