Passing a variable (coupon code) into eshop

I have an e-commerce site setup with Joomla 3.4.5 and eshop 1.3.8.

I need to set our site up so people can come to say domain.com/john and once the user checks out they will automatically get say 20% off. Others may be different discounts, i.e. domain.com/sally for 10% off. We may have a few dozen of these.

I was thinking of doing the following. I would create a simple php file ( /john/index.php) which would register john as a variable and redirect to our store page. After checkout make coupon_code's value="John" which is set up in our eshop already as a coupon.

Is that possible?

bump.

On a grander sense, we need to have a store where our distributors (affiliates if you will) will re-direct their clients to their custom url ( www.xyz.com/john ) and their customers will get certain discounts on products.

Is there a way to set up multiple store instances?

Is there any way to do anything like this?