I was inspired by jkeegan's solution and decided to use it as a base for my own.
Two curtain rods (150 cm, but I'll will buy 200 cm later), 45x45 mm and 45x70 mm wood, some screws, one hour work and I was done.
It is really easy to put together so you can carry it with you. It slides very smoothly on the rails (I used silikon spray to improve it further).
The only thing I need to improve is how to secure the tripod better. It's OK for indoor use but may be a little bit scary to use outdoor.
Later on I will add four individually adjusted legs for easier levelling the slider when shooting outdoor. It also need some pimping...
This is my "video-tutorial" and a short demo.
Remember: The password to this video is MTSFP
[ame="http://www.vimeo.com/9250828"]This is a password protected video on Vimeo[/ame]