you'd have to use a purple coin
addon offering and hope no one else opens one
I've done a fair few of the 2nd level, but I'm probably going to find the "complete 3 generators using Dark Sense" one tough since I prefer to be doing other objectives (totem-hunting, keeping the killer occupied, etc...)... not sure if I can have help doing them or not, either (ie. if I start on a generator and someone comes to join me)