How did Washburn do it? In a word, mass.

Washburn used cameras such as the Fairchild K-20 and K-22, the latter of which is nothing to trifle with. An example in the National Air & Space museum is 15" × 17" x 31", with a lens focal length of 24" (635mm), made primarily of anodized steel. I'm willing to bet that beast is 30 lbs. or more.

Heavy mass on suspended mounts allow for the camera to act as its own stabilization system, to a degree. More mass equals more inertia, and inertia is the defining property of mass to be resistant to changes in momentum. I'm sure if Washburn had used some sort of pintle or gimbal mount for his camera, he'd have many fewer keepers — the direct mount would have transmitted more vibrations to the camera body, resulting in increased motion blur.

Actually, as with everything photographic, I'm sure technique was just as much in play. You can't take good images with longer shutter durations from a bouncing mount — good weather and smooth winds are required. But in a sense, this isn't much different than lots of landscape photography. Sometimes you have to pick your days to get your shot.

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In your situation, with a flexible bellows, I would probably construct a "blimp" of sorts to completely enclose the camera (except for the front of the lens). Normally a blimp is used to silence a camera in situations where the camera sounds would be inappropriate (such as taking stills on film sets during production, or during live opera and stage performances, etc.). But in this case, the blimp is used to shield the bellows, lens and camera standards, and anything else that is less than sturdy, from the wind. Perhaps a simple telescoping box enclosure, maybe felt-lined along the telescoping parts to provide some stability and isolation. You'd probably need to cut some holes to allow access to the focusing rack. But you could provide a door, flap, or just tape over the holes when focus is achieved.

You might consider rigging a harness similar to Washburn's. You won't have nearly as much mass as Washburn's cameras had, but adding dead weight to an object is a simple task.