At home here I have two small flakes of flint picked up by a public footpath near Avebury. They come from a flint knapping site where some 4,000 + years ago someone sat and fashioned some stone tools. Ephemeral sites like this survive quite well and around Stonehenge people would have been doing the same thing. Even if they were only there for a very short time they still would have had to cook,erect shelters and dispose of their rubbish and sharpen their tools. They must and would have left evidence.
Wrong time of year to try I know but I would love to get a sheaf of corn, spread it on the ground and use an ordinary garden roller to process it. Using some domestic fans to provide the wind might give a rough idea of the feasibility of the idea.
When Foamhenge was built it was not intended to replicate Neolithic building techniques, only to see what the monument might have looked like when finished. The experimental archaeology I and many others were involved with was to investigate ways of moving the stones.
To suggest that the "missing" lintels facilitated the erection of the structure and a hopper was placed there (I thought the grain was on the ground all around the circle?) is pushing your theory a bit too far.