Yeah, should be possible, you'd have to switch the fake torch gloves with regular ones when taking out a shield though.
Fun fact, the game already has a wield left handed item flag but it only works for the main weapon.
edit: Yup, doable, needs gloves. You'd have to make new textures for torch with gloves included or it will look wooden.
Bwhahaha I will carry my crossbow in the left hand.
Still, with modifyable carry slots this would be even easier, there's enough free ones left, but I can't find them.