I did this back in March 2020. When Bitcoin had that crash almost to $3k I took one of my credit cards and did a huge purchase then did a “DCA” over the next 12 months to pay it off with a 0% balance transfer with a one time 5% fee. When BTC went to $69k it was an amazing trade in fiat terms I could have easily sold the BTC to cover the credit card but I didn’t. I just used the cash flows from my fiat job to pay off the card and kept the sats in cold storage