I did something similar with my Trung leaderhead One sister was the regular nif. The second (BG one) was the leader nif but added the BG mesh behind it. I then changed the BG kfm to show the leader's animmation. I thought about doing this for Alexander by adding a horse unit behind him that was animated but felt that the units were too low poly (and too much work to add detail) to add it. fyi with units you can also edit the animations in blender to add more too.