I could, but that raises the bar well above the target audience. Lots of people without technical interest want bitcoins. Running scripts sounds easy for me, but many people interested in Bitcoins can't be bothered to have to deal with installing the client, and are scared to swim in deep waters after hearing that hackers and viruses are after their wallet.dat's. But most people can manage "buy now with paypal", as well as deal with a credible and provable assertion that the one guy who made their hacker proof wallet isn't going to stiff them.
the problem is that it's an unprovable assertion. nobody can tell whether you've kept the private keys. all a thief would have to do in your place is keep all the data, inspect the block chain periodically for a very large balance, and strike once many years from now in an entirely untraceable way.
i actually trust you, and i doubt i could name five other members of this forum i would say that about. but sadly i would not be able to recommend a service like this.
it wouldn't be much harder to set up a website that uses the right sort of handshake to prevent you from ever knowing the private keys, and then outputs a pdf that the customer can print. why would anyone prefer the physical post here, unless they don't know how to print a document? (the post adds an additional problem, which is that the document might be inspected by a post officer or any other 'man in the middle'.)