That won't work. Since he would be on a Mavericks recovery partition, it would try to download Mavericks and once the AppleID is entered, it will see Mavericks is not attached to that account and slam on the brakes.
Sorry for my bad advice OP, I figured it was worth a shot as I can't think of any other way to add it as redeemable.
You need a Mac that originally shipped with Mavericks and has its recovery partition intact to be able to register it agains your account. Why you'd want to I don't know. It was a buggy os
If you had a Mac that shipped with Mavericks there is a work around here where you can intercept the Internet recovery installer and make a USB key that way, but that still would not associate Mavericks with the AppleID.
If you have purchased Mavericks USB via Amazon, why not contact Apple support, and tell them this fact. You can even upload Amazon purchase slip. I almost certain that Apple will open the download for your Apple ID, because it's your right to get support from Apple as software vendor even though you buy it from Amazon, and also, there is no cost for Apple by doing this.
I think you are missing what is going on here with Amazon. Mavericks was free to download from Apple. Anybody selling a Mavericks USB key on Amazon is doing so illegally and violating Apple's EULA. All they did was get a Mavericks installer and make a USB key and sell it through a storefront on Amazon. Buying this does not in any way give you some sort of claim to Mavericks from Apple.