Well... I think I know how this would be done... (I'm not sure enough to say that I'll do it though)
If you have KotOR Tool, just open up all the files for the Lightsabers in the GFF editor and add the property: On Hit: Instant Death DC 100 and then save the file with a different file name. (E.g. MyShortDeathSaber1.uti) and then use the giveitem cheat in order to get the items...
Yeah, I'm pretty sure that's all that would have to be done.