I found this out while playing around with weapon set-ups with Titan's Grip. Apparently speccing into Titan's Grip lets you put an "Off-Hand" Weapon in your mainhand.
I guess it's not so much an exploit as an undocumented change but I thought it was an interesting find nonetheless.
Searched for "off-hand" "titan's grip" "titans grip" couldnt find any post like this.