I am not sure, but I doubt it.

Certainly at my level of coding for wow, I would be unable to do it. Targeting functions are protected and so there are restrictions on using them. However look at what the author of trinity bars 2 has been able to do with that mod, all within the protected framework. So perhaps it would be possible.

This is my dream functionality. You could use a shared variable for determining your lead character and free up both focus and target for other actions.