Question about sales from your magazine's website

I'm looking for some rough figures regarding what percentage of magazine subscriptions are made through the magazine's website versus through other means (subscription cards, telephone orders, etc.) The magazine that I work for currently does not accept credit card orders online (it's a security issue, not lack of ambition on our part!). I'd love to get some figures so that I can add them to my presentation to our technology team. I know we are losing revenue by not having a way for people to subscribe and pay online. If I can come up with hard figures it might prompt the powers-that-be to devote some time and money to this problem so we can finally get it resolved.