Adding items to cart from an external source

Hello all!

I am building a module for opencart so my customers can design their own shirts. I have a question regarding how I should add the product to the customers shopping cart. My initial thought was that I would add a generic "custom shirt" product to the cart with the correct price and then add as some kind of "comment" in the code what the user has chosen as his/her fabric and so on. I there any way to add this kind of functionality to the add to cart hook in php? Any help and pointers would be greately appreciated!

Thanks in advance!

Specs:
-Opencart 1.4.9.4
-Running on Dreamhost (only during testing)