Also, I have no idea if what I'm about to propose is even possible due my lack of scripting skills. (I'm assuming a script extender will have to be involved in a mod like this.)
The idea:
Basically, bind mouse-1 clicks to alternate between left and right hand attacks and mouse-2 to attack with both (no power attack).
Then you could make it so that holding down mouse-1 would perform a power attack (dual).
Also, if possible, set a condition that the player has to be using two swords, two daggers, or one sword and one dagger.
This is all I have at the moment and until I know if it's even possible there's no point in going much further than this.
Please let me know what you think of this idea and if it's even possible.
Thanks
Gonk