Encrypted PayPal "add to cart" buttons with multiple weight options per button

I'm in need of some PHP/other code for encrypting PayPal Payment Standard "add to cart buttons" that have muItiple weight options for per item. Example: Organic Fertilizer with drop down options of 5 lbs, 25 lbs , 50 lbs. I am using the paypal shopping cart with a custom checkout view and need code to transfer the weight value of the option selected to work with my paypal shipping calculator settings. I have my own Domain and am using Weebly Pro for design. They give you the option drag and drop a custom html to the design page and add your code. This is where i've added my hosted button code and product code. So, i'm not sure if PHP,C#, etc. can be used here but I am also able to modify the main CSS and HTML code of the website. I would like to have a general template of the code to modify the values for different products and options. I also need template to include additional data items such as IPN, PDT, and succesful order return url. I can generate the SSL certificates but the code to encrypt the button(s) is out of my current scope. Must work in paypal sandbox.