WATCHMEN

1) Equip a 1h weapon and an offhand.

2) Place desired 2h weapon in top left corner, then move it down 1 slot (so that there's 1 open space above it).

3) Drag and drop 1h weapon to the empty space above the 2h weapon.

4) PROFIT.

You can also do the same exact thing with your offhand.

Dual wield 2h weaps, 2h staffs, 2h Crossbows (Shin).

You're very welcome.

Now, to debate whether it's worthy of ban due to exploit....

EDIT: While equipping a 2h and an off hand gives the appropriate stats (the damage and stats from the 2h weapon as well as the damage and stats from the off hand), equipping two 2h weaps bugs out the dps and shows a decrease. Not sure if this is because this is a bug and therefore the game does not know how to properly calculate the damage, because it averages the two weapon speeds together which causes a mathematical decreas in damage per second, or whatever - I'll have to look into it more tomorrow. However, you do receive the stats bonuses from the 2h in your off hand, so if you find one with better stats than say your orb or quiver it might be best to use this bug even if there ends up not being an increase in damage for whatever reason.