Adding actual dual wielding would require code work and at that point doing "just" daggers wouldn't be much less work than doing it for every weapon combination.
The "little work" solution to this would be to take a standard two handed weapon, give it the graphical appearance of a pair of daggers, and call it "twin daggers" or something similar. It'll function as a two handed weapon in all mechanical respects, and you might have to get creative with the model to make it work well with the animation. OTOH, this would also make it inherently balanced with two handers...
