Does anyone know how to change an npc's persistence via script?

My situation:

I have recruitable followers spawned from leveled lists. I do this to add a little variety to each play through.

The problem is that if any of these followers are left somewhere they disappear when the cell resets/respawns.

This does not happen if they are recruited and following the player. It only happens when they are instructed to "stand guard" or "break up". This would not happen if they could be dynamically set to persistent references when they are spawned..

I have tried setting the leveled list spawn point to persistent. This does not work. The documentation for the OBSE function "ispersistent" says that it is only a bool return function.

If I could set them to persistent on load I believe it would solve my problem.

Any help would be greatly appreciated.