I'm with Joe on this one - this is absolutely the toughest DL route to upgrade, and weekend flights are the worst. My bet is if you change your schedule to midweek, the upgrades will open up, but you're also VERY likely to find yourself in the back on your current schedule. I'm on the same route in a couple of weeks and got the upgrades by not flying on the weekend.
Just out of curiuosity why are you on a full Y fare? At that rate (probably over $1,600) you can buy a Biz class ticket on Korean and not worry about upgrades.