A while back, I came across this piece of information and I remembered this thread. Well, it seems PF synchronised their music to films the exact way I proposed they could have done it. It is fairly simple, really, and I still cannot understand why most people believe it is ludicrous to think they synchronised TDSOTM to TWOO.
From
http://en.wikipedia.org/wiki/Obscured_by_Clouds
At this point in their career, the band were not new to scoring movies. They had already scored the films The Committee in 1968 and More in 1969.
The band was already working on The Dark Side of the Moon during this period, but production was interrupted when the band travelled to France to score the movie. Nick Mason refers to the project:"After the success of More, we had agreed to do another sound track for Barbet Schroeder. His new film was called La Vallée and we travelled over to France to record the music in the last week of February... We did the recording with the same method we had employed for More, following a rough cut of the film, using stopwatches for specific cues and creating interlinking musical moods that would be cross-faded to suit the final version... The recording time was extremely tight. We only had two weeks to record the soundtrack with a short amount of time afterwards to turn it into an album."