I know you can use a 2-handed weapon on a single hand by not having a free hand (aka just having another weapon equipped on that hand), but it's clearly stated on the chat when you try to do what that the weapon will have an accuracy and speed penalty.
Though you can just ignore the accuracy penalty if you have accuracy bonus.
In all gameplay I do, the first thing i try to get is any ranged weapon with scooped attribute, which gives you +3 accuracy that's pretty much enough to almost never miss a physical attack no matter what's your weapon proficiency.
In my current gameplay I have a Halbert (2 handed weapon) and a Riot Shield equipped, with no extra arms, and I don't feel any accuracy penalty thanks to the scooped weapon I have equipped