For years (since gift cards stopped working), I've used Mileage Multiplier to get AmEx credit. I'd book a short award trip, buy the cheapest Mileage Multiplier option, and the credit would post 2-3 days after the charge converted from pending to posted. I'd then cancel the award itinerary.

I purchased an $80.63 MM (cheapest offered) on 12/14. The charge description is "Miscellaneous Tax(S)/Fee(S)." Credit posted yesterday, so nine days rather than 2-3, but very relieved it still works.