Kaos is correct about doing this, and you can do it but there are a couple problems.
1. it is fraud
2. he has a V1 non-hdmi console, you would have to be pretty lucky to find a non-hdmi console at wal-mart.
If you do take kaos's advice, you just switch cases as thats where the serial number is. (There is also a serial sticker that you can peel off under the front bottom USB door.)
Like I said, wouldn't reccommend anyone doing this because sometimes the wal-mart employee will call microsoft to report the serial and possibly your identity information.
A couple ways you can temporarily fix them in the convience of your own home for very cheap are;
Replace the x-clamps which hold the heatsinks to the chips, with the bolt and washer method (Search RBJTech or Lawdawgs method)
Another way is to purchase a heatgun and physically try re-flowing the GPU, Southbridge, and memory.
I have fixed a couple using both methods mentioned above, sometimes they last 1-2 days, sometimes they last 2 -3 months or longer.