4% CASH Back at Walmart through Ebates

If you are a big Walmart fan, Ebates is offering 4% cash back right now.  I know 4% cash back doesn't sound like a great deal, but trust me it will add up quick and it was only 1% previously.

Walmart has excellent shipping charges and actually ships to the store for a lot of items for free. 

Now I wonder if you can purchase items online, use site to store shipping for free and then use a coupon on what you just purchased?  You do have to pay online, but like many other stores, Walmart may just refund you the coupon difference.  Anyone ever tried this?