Interspire Shopping Cart Function Improvements

PLEASE ONLY APPLY IF YOU HAVE INTERSPIRE CART CODING EXPERIENCE. Examples of your understanding of ISC or previous ISC work will be requested! I have ISC 6.18 installed on my own domain. Shared hosting. At present all downloads are from the server hosting ISC. My customers receive masked urls. I will soon store downloadable products on Google drive, sharepoint, dropbox. So, I need the ability to add those 3rd party download links when listing products. The customer will need to receive masked urls to those products.