I don't think that you would be able to buy anything directly using bitcoin on ebay or amazon as they have not yet started to accept bitcoins as a mode of payment so then only option left for you is to sell them and exchange for fiat and buy the using COD method.
No need through cod methods, he wanna use their money to buy in online such as ebay or amazon.
Change his bitcoin into dollars is enough to buy in these. Dollars is acceptable in most popular online stores.