If you want something that dies slowly, you might be able to copy and edit blood guard settings. They lose 1 HP per month after leaving their home and eventually die off.
You cannot remove the berserk from that. Additionally, you can get it from Naedes(sp), but you cannot remove the creature having awe (and a few other abilities).
In the end I went with a solution by making the speakers have incredibly high upkeeps, so you cannot rely on the exponential unit production as easily.