I have solved the problem by bundling an external resource directory in the final APK file.
I am developing for Air for Android with Flash CS 5.5, which allows bundling of external resources in the Air for Android settings. Adding a resource folder to the list of files to bundle is easily done through the settings pane. This allows me to include sounds to be loaded from an external folder.
Air for Android Settings -> General -> Included Files
Just add the external resource directories to be bundled.