I did find a solution...

After focusing, adjusting shift et cetera my arms were getting really tired. But before resting I took a sighting along one corner of the camera, so I knew that if i pointed the camera in the same place I would get the scene I had planned.

So while resting my arms, I inserted the film holder, closed shutter, set time and aperture, mount air release. Then lift camera, pull dark slide with right hand, put it under the handy clip on the back, aim, and stomp on the release bulb.

Result: http://www.bruraholo.no/bilder/handheld.jpg