How to make additive blending (in mecanim) weight >1

I have an animator layer for the full body for walking running etc. and another layer for holding weapons or other objects. The second layer is in additive blending mode.

Now the character can walk while aiming/holding a weapon. But with weight = 1, the keyframes of layer 1 and layer 2 are averaged, causing the hands to move too much when walking. What i need is the weapon to be held ALMOST steadily. So if the weight was more than 1, i would get what i want.

Is there a workaround to get the desired effect?