In the summer, DL tix ATL-ICN-BKK op'd by KE run about $1400 in Economy. In the low season between Labor Day and Christmas you can get it for closer to $1100. Just book on Delta.com. Even if your other tix are looping BKK-->USA-->BKK, you could certainly nest a USA-->BKK ticket into one now. If you must start from BKK, you should still be able to buy DL-coded tix. If you can't buy them through orbitz, expedia, zuji, whatever for some reason, you could try a TA like www.thaifly.com or one in Bangkok.

You could also earn MQM's on KE-issued tix, but be sure not to book into KE's lowest fare class (U?), because that earns 0 miles on all partners, including Delta.

If you want Business Class, cheapest way to earn MQM's I've found (though I'm certainly open to other suggestions) is on Korean ex-LAX or ex-SFO. Tix USA-ICN-BKK can be found for under $4000. If you can start in BKK, you might be able to get it a lot cheaper than that. LAX seems to be the most competitive gateway.