Select previous word with whitespace as separators

I’m trying to replace TextExpander with some Applescripts. TE uses a keylogger to record the entered abbreviations, but I’d just like to select the word left of the caret in the currently focused text field.

key code 123 using {option down, shift down} isn’t good enough, because it uses the separators selected in System Preferences â–¸ Language & Text â–¸ Text â–¸ Word Break, all of which also include some special characters.

Non-AS and somewhat hacked together solutions are also accepted.