I am curently working on a quite large scale castle.
This pic is of one of the few finished portions: The East Tower.
East Tower by Ru Corder, on Flickr
Enjoy!
No, the twisted tubes create too much pressure for that.
They are placed into four 1x1 round bricks, that are at an even leval with the surounding ground to provide stability.
Hope that helps, and a dryad built like this would be amazing!