How can I restore just a few files to an iPhone from a backup?

I have an iPhone backup on my computer and I'd like to restore just a couple of files. (I already know which files I need, even though their names are obfuscated.) The backup is very old so I don't want to just restore the entire thing, which is the only officially-supported action. What tools exist to do this kind of thing? I'm not willing to jailbreak my phone for this.