So how tall is Mr. Barbie Bike? I'm 6'3" and can barely stand to ride most BMX bikes.

You should buy a similar cheap, pink kid's bike, saw the tubes in a straight line and epoxy some hinges on the tubes. Fold it up and take it to work and lock it where he usually locks his bike. Leave a not telling him that he will be more comfortable on that until he gets his real folder back.

Either that, or find a longer seat post that would fit the Barbie bike and change it out while he's at work.