...that reports as "Flexible Spending" to the CRAs (because it looks way cooler, no other reason). Off the top of my head, this rules out Citi DC (WMC and WEMC). BofA has a couple of co-branded CB WMCs, but those don't count. I wonder if it's possible to get the BofA Cash Rewards as a WMC instead of VS...
Can you guys think of any others?
Did you have to wait a year before PCing?
My BoA Cash Rewards WMC also reports as flexible spending account, on my credit reports. I also have a Citi TYPref WMC that reports as a flexible spending account as well. J/c though, is there a reason why you don't think Citi DC WMC/WEMC would work in that regard; haven't some of the posters on the forum mentioned that some DCs have been successfully coded as flexible spending accounts, on their credit reports?
From what I've gathered, the only ones that report as "Flexible Spending" were PCd from other cards to DC. I've asked a couple posters thru PM, and both said ther DC WEMC cards reported as "Credit Card". I've asked a few others but never got a straight answer from them.
@thelethargicage wrote:...that reports as "Flexible Spending" to the CRAs (because it looks way cooler, no other reason).
ROFLMAO 
I've considered the Arrival cards, but the truth is, I just don't travel. Not to mention the inferior redemption rate for cashback is a deal breaker
I know you specified you were interested in a MasterCard, but if you really want a card that reports as a "Flexible Spending Account" the QS Visa Signature cards report that way, and as you know they're not too difficult to qualify for.
I'm assuming Venture Signature cards report the same way, but I can only personally 'vouch' for the QS.
Sorry I can't be of more assistance. 