Don't do it. Last year some people tried to do this and it worked with checkout, but they didn't get no rebate. They are very strict to the rules. Besides, MSN is basically just a referral site, as it ebates, so you obviously can't have two referrals going on.
<< I guess you can't take advantage of ebates or fatcash. I just ordered a nikon coolpix995 through photoalley. After I put it into my cart, I log in ebates and tried to check out with the ebates banner on top of the window. But after I clicked "checkout", it told me there is nothing in your cart! The same is true for fatcash. >>