Play one animation on top of another

Hello. I have a skeleton that is animated and has a walk cycle, an idle cycle and other movement/idle animations at various stances. I also have animations for holding, firing and swinging weapons and tools. The firing and swinging animations only use the arms part of my skeleton but the movement/idle animations use all the skeleton. My question is when the player has a weapon/tool equipped how can I make the skeleton play the arm animations associated with that weapon/tool whilst still playing the movement/idle animations on the rest of the skeleton?

The key function you will need is this.

This allows you to play a limited subset of an animation- it will overwrite any animtationstates that are not set to use those transforms in particular.