Wirelessly posted (MOT-Q9/01.09.28DR Mozilla/4.0 (compatible; MSIE 6.0; Windows CE; Smartphone; 320x240) Opera 8.65)
If you find capable agent, it can be done. I have done it on a TPAC flight. In your case, if upgrade space of the return flight is wide open, I would change the flight after the outbound.