One strategy involves a swapset to hide the existing arms and broom and create a second set of arms and broom. This second set of arms is actually a *single* arm artwork layer with a hidden/transparent patch between the two sets of arms- think of it like a monster with a single huge arm on the front of the body attached to the middle of the shoulders, with pins and sticks etc to weld it to the shoulders. The broom is included in this layer as well, with a stick down the broom handle. So you are really dragging one arm that visually looks like two arms as there is a transparent bit in the middle. Sticks go on the artwork for both arms so things flex only and elbows and wrists etc.
The other way is basically to carefully record the second hand with keyframing and dragging. But personally i never found a way to attach two separate hands to the same object. Everything needs one parent, so the arms cannot be a child of the body and broom at the same time