An idea similar to my previou post "Short Blade Advantage"
Have a skill called Ambidextrous, which allows the player to add a weapon in the Shield spot. At first, that 2nd weapon has a bad hit ratio, but the higher the Ambidextrous skill, the better it becomes.
You would also need to add the skills that represent the weapons: if you want a blade and an axe, you should take Swords and Cleaving skills. Most people will probably take one weapon skill and have similar weapons in each hand, but let them decide.
Problem: it could easily break the game if not properly balanced, and make the player way too powerful. This might be hard to code properly and not worth the headaches.
However, I think that this idea is still valid for Short Blades (see my other post), as they aren't very useful otherwise.