I just used Delta miles to book flights in F on SQ from LAX-SIN-DPS X BKK-SIN-LAX for travel next February 2010. F was avaliable on the LAX-SIN SQ11 and SIN-LAX SQ12 segments but I had to accept Y on both the SIN-DPS and BKK-SIN segments because J was not available.

The worst part about this is that I don't get lounge access prior to the Y segments.