Getting a little pricey now I see.

You have 2 obvious choices:

1) Go with the M ticket and SWUs to upgrade. But this needs 'Z' inventory to upgrade, so you need to check this as you book (particulary on the long legs) . Unfortunately this will take a stroke of luck for you as you are constrained on dates I assume. That will leave you plenty left for an K fare domestic if you want to burn a couple SWUs.

2) Shop (any airline) for a cheap fare from the west cost. You can find these around $4K or less. If you see one that works but is on a lesser known (for you) airline you might want to post a Q on the "Other Asian" board.