Metabolisms don't differ as much between individuals as many think. You could use a simple BMR calculator and it will basically be accurate.
People who eat themselves sick but don't gain weight, do not not gain because of a blast furnace metabolism, but because they can't sustain high intake every day, just like bhank. It is always true.
Of course there are pharma solutions for increasing calorie intake. Megestrol, MK-677, mirtazapine, perhaps boldenone, weed. If someone would stack those they would gain weight without even trying, doesn't matter if they have a "blast furnace metabolism."