Billing Address needed not shipping address ?

My site will just provide downloadable products, with that said the “Shipping” address is really their email address, however I still need their billing address for authorize.net.

The only way I can find to get the billing address is to select those fields under “Shipping” but when you go to the check out page it stats the billing address as the shipping address and so it applies a bit of confusion for my customers.

Is there a way to ask for just their email address in the shipping but then ask for their billing address separately?

Again on the customer shipping info I just need their email address but for billing via authorize.net I need their complete billing address.

Thanks for your assistance.

http://wordpress.org/extend/plugins/yak-for-wordpress/