I am assuming that when you say, "I'm not in a position to meet that kind of spend requirement just now", you actually mean that you don't have any need to buy $10K worth of stuff; not that you are financially constrained (otherwise buying and sitting on $10K worth of gift cards wouldn't make sense).
If you pay US taxes, you can use your AMEX card to make estimated payments. The service charge is around 2.3%, give or take. If you overpay then you can get a refund when you file.
I have paid estimated with my Visa and gotten miles. Haven't tried AMEX so I can't say whether they treat this as a purchase or cash advance. Others probably have some experience with this and maybe they'll chime in.