Secure the front fork by drilling holes through the headtube and sticking bolts through so the steerer doesn't move.
Cold set the rear bike's front forks by spreading them out so they fit over the front bike's rear forks/dropouts, then put the "middle" wheel in and use the rear wheel axle to hold the whole thing together.
Run a drive-side timing chain from the front bike to rear bike's crankset. The front derailleur is removed, of course, as are both derailleur's from the captain's bike.
The drive chain is run from the rear bike's other chainring to the rear bike's rear derailleur.
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Could be the angle but that photo looks Photoshop'd: th lighting on the bike white wall tire is the most glarring sign, also the lighting of the blue (bright and clear) on the front bike and the yellow (dull) on the rear bike don't match. Oh well, perhaps I've been hanging out in the grassy knoll too much but thats what years of working at Adobe will get you.
One problem I see with this, what happens on a big speed bump? Or a huge dip? Or even normal uneven pavement to a lesser extent. The two frames will rotate against each other pivoting at the middle axle. Maybe some type of bushing or bearing setup would make this better.