I think your idea would work just fine. Getting the straight, even line will be tough, but I'm sure you can manage it.
I've got awkward ceilings as well, and am not looking forward to painting the 2nd floor. The plaster curves from the ceiling into the wall, with no break. Even better, it won't work to put crown molding up as a break point. Currently, the walls and ceilings are the same color and I hate that too.