If you are planning to buy directly from AMEX, they won't count gift card purchases towards minimum spend (at least at last check). There are a number of tactics discussed in here for manufactured spend you could pursue:
https://www.flyertalk.com/forum/manu...-spending-719/
Honestly IMO it is not worth your time or effort for FO.
The DL AMEX Plat gets you 95% of FO benefits (MC1, free bags -- just no free preferred seats or C+/F upgrades) and you are better of just saving the money and time to buy up to C+/F on the flights you are taking next year -- and as an FO you would only get F very rarely so really it's just buying up to C+ which comes with perks that exceed the FO benefits anyway