seriously just go to walmart or circuit city. i know for a fact it works at both places. i've done it countless times.
if you go to walmart make sure that they have the games you want to get, because without a receipt you get store credit & it would be kind of pointless if they didn't have the games you wanted.
as for circuit city. go to the customer service & tell them you got them as a gift & it isn't what you wanted. as long as they have those games on the self they will take them.
so no receipt needed. like i said just say you received them as gifts and you don't want them and you'd like a different titles. you will have no problems. promise =]