I'll be the first to wish you luck... but man, I believe the model is flawed because someone can charge back their "loading" of the account with you, they don't even need to "charge back" with webpasscard. Unless you've obtained a signature, WPC hasd no charge back rights with any credit cards. In my opinion, if someone is funding their WPC with a credit card, you are almost a non-entity in the consumer's eyes and you'll have just as much of a challenge with chargebacks as if they were straight up buying the membership directly from the porn site.
Finally... You can't tell me how your function is any different than that of a 3rd party biller like Paycom, IBill or CCBill except for the fact you're potentially "storing" some value for the consumer. That being the case, in my opinion, you are ultimately going to be subject to the same rules and regulations that those IPSPs are and trying to circumvent that will be perilous.
If it were this simple to get around chargeback dilemmas, merchant registration with Visa/MC, to accept American Express - all of the above mentioned companies would be doing it. I am skeptical but I wish you luck nonetheless, perhaps there is much I don't know and you'll prove me wrong.
In the interim, I'd have to assume many 3rd party billing companies will be raising the red flag for Visa's radar. If that is the case, ouch. By your own admission, you've been TMF'd so if you're an owner in any way of this business then you aren't allowed to even have a merchant account.
Cheers,
Brad