I routinely "nest" flights on my RTW's. I'm in the midst of my 4th RTW orginating in CAI. (I finish one and start another). I flew MIA-BKK on continuation of my RTW in January, then cashed in miles for a nested F/C ticket BKK-MIA-BKK. I will be home for several months in MIA, then resume my RTW in BKK. I did this last year, and was able to purchase a B/C ticket on SQ airlines from CMB-SFO-CMB for approximately $1,600.00. (Then purchased another coach ticket SFO-MIA-SFO for about $275, and received complimentary EXP ugrades). This allows you to break up the trip and return home, then continue with your world travel. I haven't had the brains to do 2 nested RTW tickets --- yet!

If you purchase tickets, it is much cheaper to purchase J BKK-SFO/LAX-BKK than J SFO/LAX-BKK-SFO/LAX (or CMB). I played around on ITN.