DY: That doesn’t make any sense. I agree that it’s not impossible to hold that there is an individual Chiyuv, but if you hold that you need a Melech, then you by definition can’t hold of an individual Chiyuv. Killing an individual Amaleki might be a partial Kiyum in Mechiyas Amalek, but even if it is it only stems from the general Chiyuv, which the Rambam holds is nonexistent without a Melech.
And I would have a heck of a problem with a Yeshivah student, even one of the Chassam Sofer’s caliber, Paskening a life-and-death Shailah on his own.