You don't actually have to. If one of the three people happens to DC after you've hit "enter" for the zone and before you've zoned in, they won't be transferred inside and you'll end up with fewer than 3 people. Their permit also will not disappear.
Hammerblow -> Powderkeg -> GG3 -> some gears -> Boss is a very easy dualboxed Salvage run, if the third person happens to DC. Here is a guide.
