The only way I see this working is if you play multiplayer.
I'd advise against this. Anyone can gangbang PW2, it's much more satisfying to do it solo. All gangbanging will prove is that you are completely incapable of handling PW2 alone, and it takes the sum of you and your team to equal one PW2. It means you're not its equal. Gangbanging should be reserved for farming AI boards and mech parts after you've already killed it yourself once before.
Just bring the strongest missile launchers you have access to, and chaff grenades may work on it (I don't remember). Chaff is meant for disabling its EM pulse, so don't waste those. Chaff won't work on PWCustom, though. I don't know if you have access to the Outer Ops for the battle helmet, but get that too if you don't have it. Obviously, aim strictly for the AI pod for maximum damage. Stopping its nuke launch, though, may be better if you target the nuke launcher itself. I don't remember.