The only way i see this happening is if the char have animations for it..
as for main and offhand, thats same as right or left hand..
Dual wielding again if char has animations for holding something with 2 hands.
I'm sure if u make your own chars, you would do your own animations for weapons..
I'm not sure on the pre-build char system on what they have.
maybe an Alpha tester could answer this.