In the past I have made sorting routines for Sanskrit and other Indian languages, which has the same alphabetical structure as Lao (Lao script is actually a derivate of the Indian script system). I found it much too tedious to try and sort the Indian script itself, represented in Unicode, but instead I first had Perl change the text into a Roman transliteration, sort it, and then turn it back into Unicode. Of course, you must make provisions to move prefixed vowels to behind any consonants in the transliteration. Then I think BrowserUk's second approach will work just fine (I myself used a much more crude and inelegant solution).