I suggest to use this solution.
But I changed definition to this:
    public ThemedViewEngine()
    {
        base.MasterLocationFormats = new string[] {
            "~/Views/{1}/{0}.master", 
            "~/Views/Shared/{0}.master",
            "~/Themes/{2}/Views/{1}/{0}.master", 
            "~/Themes/{2}/Views/Shared/{0}.master",
            "~/Themes/Default/Views/{1}/{0}.master", 
            "~/Themes/Default/Views/Shared/{0}.master"
        };
        base.ViewLocationFormats = new string[] { 
            "~/Views/{1}/{0}.aspx", 
            "~/Views/{1}/{0}.ascx", 
            "~/Views/Shared/{0}.aspx", 
            "~/Views/Shared/{0}.ascx",
            "~/Themes/{2}/Views/{1}/{0}.aspx", 
            "~/Themes/{2}/Views/{1}/{0}.ascx", 
            "~/Themes/{2}/Views/Shared/{0}.aspx", 
            "~/Themes/{2}/Views/Shared/{0}.ascx",
            "~/Themes/Default/Views/{1}/{0}.aspx", 
            "~/Themes/Default/Views/{1}/{0}.ascx", 
            "~/Themes/Default/Views/Shared/{0}.aspx", 
            "~/Themes/Default/Views/Shared/{0}.ascx" 
        };
        base.PartialViewLocationFormats = new string[] {
            "~/Views/{1}/{0}.aspx",
            "~/Views/{1}/{0}.ascx",
            "~/Views/Shared/{0}.aspx",
            "~/Views/Shared/{0}.ascx",
            "~/Themes/{2}/Views/{1}/{0}.aspx",
            "~/Themes/{2}/Views/{1}/{0}.ascx",
            "~/Themes/{2}/Views/Shared/{0}.aspx",
            "~/Themes/{2}/Views/Shared/{0}.ascx",
            "~/Themes/Default/Views/{1}/{0}.aspx",
            "~/Themes/Default/Views/{1}/{0}.ascx",
            "~/Themes/Default/Views/Shared/{0}.aspx",
            "~/Themes/Default/Views/Shared/{0}.ascx"
        };
    }
Default theme is default so it is required to exists.
Structure of directory will be:
- Content
- Themes
- Default
- Content
- Views
- Home
- Blog
- Whatever should be skinned
 
 
- OtherTheme
- Content
- Views
- Home
- Blog
- Whatever should be skinned
 
 
 
- Views
- Articles
- Posts
- Users
- Settings
- Other Administration stuff