Mecanim Animation Re-targeting [Involving Extra Bones]

Hey, new to the Mecanim system and looking for a few tips.

I have 2 humanoid characters, 1 which i can edit and another which i cannot edit. the one which i cannot edit has been rigged and animated with an array of actions that include a sword. the one which i can edit is rigged slightly differently and has no animations.

What i'd like to do is edit the non-animated ones bones structure in such a way that i can apply the sword animations to it using Mecanim. Is this possible? Could you give me an idea of how to go about doing it step by step? Any help you can give me is fantastic.

Extra information and limitations: I am using Blender for rigging/animation of the non-animated model if that changes anything. I cannot simply parent my sword object to the hand of the non-animated one and apply the animations from the original (since Mecanim is smart enough to map all the body motions) because there are various sheathing animations as well.