More cheating on the Tour de France?

[JuliaL]

How does this motor work again?

These bikes mostly use off the shelf, albeit top of the line, drive train components.   So any deviation in shape of drivetrain components will be instantly picked up cycling gear heads.  So there is no room in the bottom bracket or wheel hubs to hide any rotory motor.
You can't put a motor anywhere else and transfer the torque to either hub without something highly visible on the outside.  

So The only way i can think of is to create a sort of linear motor embedded in the chain or rear stays that move magnets embedded in the wheel rim. Is there enough room in a bike's chain star or seat stay to hide a set of stators of a linear motor.

I saw the segment.
Looked to me like it was a cylindrical brushless DC which fit into either the seat or down tube and drove the crank axle via a very coarse worm gear. I would also expect it had an overrunning clutch but that wasn't as obvious. Could also be that they idled the motor at the riders cadence when not trying to drive the bike, but that would be more complicated and failure prone.
Battery is also packed into the tube.  Didn't see/don't know how they charged the battery, but it seems that would be pretty easy to hide as a stud or rivet head which didn't look insulated from the rest of the frame but was.