Unfortunately, there really isn’t a way to do it the closest you can get is.
-Remove all programs from the add/remove programs list
-Remove anything you manually installed/downloaded
-Create a new user profile and delete the old one. (To remove any temp files, saved settings and such)
If for some reason some one really wanted to though it wouldn’t be hard to recover most of it. If it’s a non issue and it needs to look “fresh” then the above will do it.