I am flying a friend BKK-DXB-IAD-DXB-BKK in July on EK. I will be flying with her DXB-IAD in paid J and wish to only purchase a Flex-plus DXB-IAD return and upgrade her only on those legs. She will have a 90 day layover in DXB on the return.

I tried to book this trip online but it only lets me bundle the legs BKK-IAD return, I don't have enough miles to upgrade the entire trip. Any way around this after they are booked or by calling Emirates?

Anyone with experience on this flight can tell me how easy is the upgrade, I am intentionally staying away from ORD because it is usually packed in J (777) and IAD is an A380.