2CO has been reported today that now they officially support payment method of PayPal. Read more in this article:PayPal at 2Checkout
That actually means (or it's supposed to be) that you can enter your PayPal account info upon the order and purchase the add-on(s) without entering your CC information.
I have not tried it myself, but if somebody of you will have problems with it, please report it here, and we will forward your issue to 2CO.
No additional or hidden fees from our side are applied if you pay by 2checkout.