Help - Horizon-like Portrait->Landscape app

I'm looking for a service - either online or in the form of an iOS / Mac app, that would take a portrait photo and make it landscape - not by cropping, but by adding a background that is the same photo blurred or darkened etc.
(Sort of like TMZ when they don't have a good photo to work with)

If any of you are familiar with the Horizon app's video extension for iOS, I'm looking for a photo version.

Thanks