I work as a private consultant and I do this when I bill my clients all the time as most places of employment or clients only want a receipt. I tell me clients I do this, and frankly they see nothing wrong with it as they are just reimbursing me for airfare they would have had to cover anyways. If your client or work is paying, the method of payment you use to acquire your ticket should not matter.

As a strategy I normally do this at the end of each one once I reach my maximum status for an airline. So for example, if its December 1 and I've reached 1K on United, I'll likely book the rest of the month's (year's) trips with miles so I can pocket some extra dough.

I'm not suggesting anyone deceive their employer, but frankly, how would they find out unless you performed the transaction on a company credit card? If I book a flight in dollars, get a receipt, cancel (and get refunded) and then re-book the exact same flight using my miles how would my employer found out? I would have a receipt, and copy of my boarding pass. They wouldn't know to look for any refund or credit.

By asking that question, you are indeed suggesting that fraud is OK as long as you don't get caught.

And it is very easy to check. I know first hand that my accounting department randomly audits plane ticket receipts by verifying with the airlines if the amount on the receipt is correct. In many cases, they can do this online with the receipt you gave them (e.g., your first+last name, record locator number, eticket number).

An update: So last time, I simply didn't use any miles and went with the economy ticket.

But I'm facing the same dilemma again, because the company has asked me to move, and I'd really like to use my accumulated miles for the big move.
I guess I'll have to talk to the HR about what the different requirements are.

As before, the options seem to be:
1) Fly economy
2) Get upgradeable economy and upgrade to business
3) Book a separate economy reservation that is refundable and cancel the ticket, book a separate award booking (need to investigate whether the HR is okay with this)
4) Book a separate award booking reservation and get reimbursed for lowest advertised economy fare.
5) Book an award reservation and get reimbursed for the fuel surcharge + taxes
It'd be most straightforward if I could just get reimbursed for the lowest advertised price, but I'm not sure if that will fly.

I would think that 5 - reimburse for the lowest coach fare, which is likely what you'd pay according to most travel policies I've seen - would be easiest. It's the equivalent of 1, no? Everything else is likely more expensive.

Yeah I think I'll have to go with that.
I guess there's no way they'd reimburse me for a full fare of economy if I only used miles.

The receipt and the boarding pass will have a different confirmation number (record locator) and ticket number from each other.