I'll add this to the list of requested improvements to the SSA Importer script (http://www.aenhancers.com/viewtopic.php?t=247), although I'm not sure when I'll next have time to update it.
For now, maybe you could jump to each keyframe and use the 'Split Layers' command?
Just to let you know, I've posted a new script called SSA Karaoke Animator which should do what you want. (ie. each word/syllable is on a separate layer) http://www.aenhancers.com/viewtopic.php?t=380