Can't you simply sell them something different instead so they never get charged for porn in the first place?
That sounds like a good idea; just handle the cascading yourself. Couldn't you sell access to - say - some music site or sell bitcoins and - as a kind of "bonus" - give access to the porn site itself? Just hide the main product behind something innocent like a premium account or something that won't raise eyebrowses from spouses.
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