Integration of discount code capability into PayPal Minicart

We currently use PayPal MiniCart, but it does not handle gift certificate/coupon/discount codes. We have searched around for e-commerce shopping carts but are unable to find one that fits our exact needs. Ideally, we would just like to find someone who is good with coding and that can quickly integrate the simple and secure capability of using discount codes into our existing PayPal MiniCart. Our overall needs are: - Integrate into our existing shopping cart design (look and functionality). - Handle discount codes (up to at least 10 digit alphanumeric) in the storefront. - Securely, and easily, handle the storage and input of discount codes in the back end, including ease of setting parameters of each individual code. - Have product options in drop down boxes that effect pricing (such as size of product), as well as checkboxes and/or radial buttons that effect pricing, if possible (not a necessity). - Able to handle the upload of a file, and uniquely tie that file to that particular order. - A "floating" semi-hidden, pull-down "Your Cart." - Able to seamlessly transfer all the required data to PayPal for checkout. - Not require any login/registering, including guest checkout, or even show the option. Customer should be able to proceed through the purchase process without ever being asked to sign in/register or continue as a guest. These requirements can be accomplished by one of two ways: 1). Code/program a complete shopping cart from scratch that meets all of the criteria; or, 2). Code/program the use of discount codes to work with our existing shopping cart. Again, ideally we would prefer option 2). as it will be the least expensive and quickest to implement. We are getting close to going live with a new product and site design, so it is imperative that this is done as quickly as possible, while still be of good quality and completely secure.