Well turn on Simulation and Simulation Generates Hit Event. Rest stays the same from my Solution the only difference is you also Provide the Bone you Hit to the Impulse. Here as Example I add a Impulse the applies a upward Force to the Bone that has been hit. Screenshot - 3fb12012fdccf9aa879eb47ba7863c2f - Gyazo
Alternativly you can start with the Simulation off and enable it on Hit and than apply the Force making your Target basicly a Ragdoll on Hit. Or like in the Docs mentioned only enable Simulation on the Bone you hit and all its Children like from Shoulder down to the Fingers.