Hey.
For this you need 4 pieces of tier 10 and an equipmentmacro-button which equips your pvp/other gear.
Basically it requires for you to pop mirror images and swap to pvp/other gear, BEFORE you get into combat (since you can't switch gear in combat ._.). You will maintain the "Quad Core" buff you get from the 4set bonus, even after you swapped to pvp/other gear.