Set maximum resolution in Windows 8.1 store app

Hi,

My game is designed to run in 1024x768 resolution. I don't want resolutions higher than that. When building for Mac/Windows desktop, I use windowed mode to ensure the resolution is always the same. However, I want to ship for Windows Store as well. It seems I need to use the "modern UI" if I want to be in the Windows Store. However, this forces my app to go full screen and use a higher resolution than I want. How can I restrict the resolution to 1024x768 in the modern UI? I don't mind if the game is scaled up, but I don't want more pixels used. I tried using SetResolution, and it works except it forces the content into the upper left corner of the screen which is ugly (it would be fine if I could somehow get the content centered in the screen).

Thanks.