I made one myself, and wound up changing NPC control to mage. (This was Library of Segrob, in case you're curious.) In response to your question, there doesn't seem to be a way (knowing what we know now) to not restrict it to a class, and yes, you have to keep your PC alive.
If any of the hackers want to play with this, we could try to find the class variable and the test (probably 'equal to') near the leader class bytes, then make those available for change. Even if we can't find the class variable, if we change the test to 'greater than or equal to' we can just set the class to 0 and then all classes will be able to control NPCs.