Spawn 3 plasma pistols (or any duel-wield-able weapon) and spawn a different duel-wield-able weapon.

First hold a plasma. Then as your secondary, hold your different weapon. (Primary: plasma Secondary: different weapon)

Holding your secondary weapon, duel wield with a plasma, now when you do this, it will give you the option to change you duel wielded weapon thats on your right hand, now press RB and pick it up, then press Y.

If done properly, you should have a plasma as your primary and another plasma as your secondary.