Like he did with Corpsetaker you mean? No trial, no fight, just shot in the back of the head?
Nope. That was still a combat situation.
Think
execution. The warlock is tied hands behind him/her (knowing Harry's luck, more likely her, and probably a young kid to boot), blindfolded/hooded, 100% helpless. It's not a fight, it's Harry having to
kill a helpless human being in cold blood, the way they beheaded the Korean kid, or Morgan would have had to behead Molly if things had gone the other way. Though I suspect Harry might prefer to use a gun, if has to do it at all.
The person to be killed is not an immediate threat (though he might be if he gets loose), just a physically and magically helpless human who Harry Dresden has to terminate.
Wardens do that, it's part of the job description, and I strongly suspect Harry will find himself in a situation at some point where he can't get out of it.
The closest thing Harry has done to this, so far, would be killing Lloyd Slate. That would
approximate it. But even that was not quite the same.