I really have no idea, but it's a VERY new thing that brokerages even report this information. The 1099-B can't be more than a decade old. You used to have to track it all yourself. I suspect you can use your own cost basis method. (subject to rules; of course you have to be consistent)

That said, this is definitely not tax advice, and even if it's legal/allowable, you're almost certainly more likely to be audited if your numbers don't agree with what the brokerage reports.