Play animation relative to current node position?

Hi,

I have setup a 2d character based on sprites. The character has a gun and follows the mouse cursor with head and arms. I have done this using 2 different keyframes (from 0 degrees to 90 degrees aim range) and setting animation time manually. This is how I interpolate the pose and get the correct angle to the mouse cursor. Now I need to add a shot animation where the arms, etc... shake a bit to fake the back power of the shot. Is there any way to play this animation relative to the current pose of the character? I mean if arms are at 45 degrees they will move relative to its world transformation (arm will move backwards through x negative axis direction).

Could anybody point me in the right direction?

Thanks in advance.