My guess is yes. Hospitals do this where I am. When someone is going to die in short order, say from cancer, they will up the morphine to the max for pain relief. Its a humane way to end their suffering. From my observation, the person is out of it, no longer in pain and eventually goes to sleep permanently. They use intravenous.
They aren't *killing* anyone (technically they are), because the cancer has already done that.
I use cancer as an example because I've known a few people to die in the hospital this way. They couldn't deal with the pain anymore, so they essentially went to the hospital to die.
As far as how much, and sourcing morphine, I have no idea how challenging it would be. It would be dependent on your location. Nembutal for example is a no go unless you're able to travel to the very few places you can get it.
SN became a popular option because of this, but even that is likely to become hard to get due to its popularity.