I'm flying to Hong Kong later this year, probably on CX. I'm preparing to book the flight.

My employer will reimburse me for ordinary Economy, but not Premium economy. Here's what I want to do:
- on one receipt, I buy an Economy ticket. I will give this to my employer for reimbursement.
- on a separate receipt, I upgrade to Premium Economy. I will pay for this out-of-pocket.

Is there a way to do something like this?

I have AAdvantage Platinum status, but I doubt AA status will help me with this...

I tried searching for answers about this, but I didn't really know what keywords to use.