How can I build a LEGO marble pump? All right, here's a tough one for ya'll.

How can I built a marble pump out of LEGO bricks? What would the mechanism which pushes the marbles up need to look like?

Here's an example in this video:
http://www.youtube.com/watch?v=OBb-qyXFb5E&amp;feature=youtube_gdata_player

Unfortunately, one cannot see the mechanism which pushes the marbles upward very well. I couldn't determine what pieces he was using - I think there was a slope, but I'm not sure as to how it moves the marbles up the pipe.
A pump is one of the most classic GBC (Great Ball Contraption) modules but is indeed difficult to get right.

One of the best illustrations I know is on this site:



Unfortunately, most of the site is in German, but the pictures are usually illustrative enough and I think it's a good source of information for ball machines in general, not only LEGO ones. The best is of course to get in touch with one GBC builder at events and ask for information.
EDIT:

Here is a picture based on the model at aforementioned site: 

Here is a video showing the mechanism in action.