Hi, I happen to be in this situation today and just had a eureka moment.
The pole has a button inside of it that the lever of the seat pushes to allow you to adjust it. So here's what I did:
Step 1) Remove the seat and the upper part of the pole (the pole has 2 parts and the one attached to the seat is like a sleeve and the other part of the pole is attached to the base).
Step 2) Take the pole that is attached to the base and turn it over. (We're using the ground to keep the button pushed in).
Step 3). Next put your weight down on the base (but carefully in case it gives suddenly). You may need to push down a few times before it gives.
* PLEASE NOTE: Our chair needed a bit of pushing before it gave. We also moved it up and down a few times to break it in.
Also don't worry if it slides back to the highest setting, it has to do with the release button not having the quick 'stop' and 'go.' It should be fine once you've assembled it back together.
Hope this helps!
Caroline
November 2012