Change Product Variation dynamically

The core of my problem is to figure out price variations based on quantity of a particular product. I was trying to make use of using variations to accomplish this.

I got stuck at the inability to dynamically change product variations, i.e., after the product has been added to cart.
Also, Is there a way to change the same via the code, if not the user interface?

Thanks,
Im

http://wordpress.org/extend/plugins/woocommerce/