Yes, you can.

As you said, you "normally" enable ONE entity to be controlled as physics entity. Now, if you want to enable a bone skeleton, you have to re-create the bone structure first. That means, you translate the bone setup into a hinged physics structure. You create first all bone nodes (as boxes or spheres) at the bone positions. Then you connect them one by one as it is defined in your characters bone-skeleton layout.

After recreating the skeleton, you have to disable the whole physics skeleton first. When you want to enable bone physics on your character you have to move the bone simulation first into the appropriate position (circumstanced by character position and animation frame). After posing, you enable physics and disable the whole (scripted) character control (which would affect movement and animation, etc.). While the physics skeleton is being "active", you would run a additional routine that checks the physics skeleton and its node positions. In each frame you have to reset the model and move each bone (beginning at the base-bone, because all others are affected) to the related physics node entity of the physics skeleton.

The whole thing is relatively easy compared to the bone movement and rotation, because bones are driving me mad - remember that each bone (no matter which position it has and which rotation has a 0,0,0 rotation and a 0,0,0 position when resetted. This is absolutely weird and makes everything more complex as it has to be.

I hope you got the idea.