Globalization and resources files, fall back to another file when resource blank

I'm using Globalization and resources files in a 4.5 C# asp.net web forms app. It all works very well. But I was wondering if there is a better way to manage items when one is missing. I.e. I use a custom set of language files and every once and a while one is not translated. so when the user gets to an area inside the app with that label (for instance) it is blank.
How can I default back to my English res file if the language of choice is missing that item?
Code:
Thread.CurrentThread.CurrentUICulture = CultureInfo.GetCultureInfo(sLanguageSelection); lblSomeTextBox.Text = Resources.myapp._255.ToString(); Label 255 in English file is populated, in other languages is blank. I would like to "fall back" to English when blank.