Add ccbill payment gateway to my Paid Downloads WP Plugin

Hello, I am currently using [login to view URL] to sell downloadable vides on my website [login to view URL] I really love the simplicity of the plugin and want to keep using it. The issue is that the developer has no interest to add the CCBill Payment Gateway as a payment option and I woulod like to do that my self if possible. I never hire any developer before so please get back to me and let me know how things works! PS: I atached the plugin file so you can check the code.