This won't work as-is for the shortcut. You'll have to edit PPSSPP.rc in order to make ID_OPTIONS_SCREENDUMMY use "Z" and then uncomment the ID_OPTIONS_SCREENDUMMY case @hrydgard commented out. After that, you'll have to use some sort of incrementing counter that keeps track of which resolution you're on.

Something like:
```C++
case ID_OPTIONS_SCREENDUMMY:
{
    static int resolutionMultiplier = 0;
    resolutionMultiplier = g_Config.iInternalResolution <= 5? ++resolutionMultiplier : 0;
    SetInternalResolution(resolutionMultiplier);
    ResizeDisplay(true);
    break;
}
```