There is no bone feature in Construct 2, you could use Spriter for bone animation.
But I think a solution for you would be 2 (or more) separate sprites that are pinned on each other.
So you would have a sprite for the lower body containing all the leg movement, and an upper body sprite that holds the weapon.
Give both sprites imagepoints on the waist, and tell the torso sprite to set it's position to the imagepoint of the leg sprite. You could also use a Pin behaviour for this.
You could even make a separate sprites for the head and weapon, this way you could easily change them in the game.
Hope this helped
EDIT: I'm sorry you are not working with C2, I stumbled upon your post while searching the forums for other stuff. I don't know if my information is relevant for CC, but I think it's a general solution.