I went to a nearby Samsonite outlet store, and the widest hard case they had is 21". The Brompton fits, but the ends definitely are wedged up along the sides: there is not a lot of leeway. I even tried some soft cases, but because the fit is so tight, there would not be a lot of room for extra padding or protection (e.g., corrugated plastic).

So, I figure I have three options:
1. Order the B&W case, assuming the latest models weight 17 to 18 lbs. as the existing ones reported. Expensive option, particularly since I'll get charged duty crossing into Canada.
2. Beef up the Brompton soft-sided case with more padding and an internal frame. I wish the soft sided case didn't look so... odd. I'm sure the check-in staff will ask. I rather not explain and hope to not get charged for a bike.
3. Use the cardboard shipping box (or something similar to avoid all the bicycle text printed on the sides). Hey, it's cheap, is within 62", and can be modified/beefed up easily. Just bring along a lightweight, collapsible wheeled luggage rack. I read somewhere that somebody just used the shipping box the Brompton came in when traveling...