I just paid my taxes with a new card to hit minimum spend for bonus (will actually pay again in March with another card and hit 2x min spend). It's going to cost me an extra $70-80 or more vs buying debit on sale at OM/OD@5x or doing the SM route and paying with those, but it gives me peace of mind that I can work with CC company if there is any issue with payment.
Have you thought of opening something new up (Airline card/hotel card/etc..) that you can use for this spend?