I'll try to help you, but I'm not sure if I can. I'm currently traveling for X-mas and don't have a dev-pc on hand to try out my theory.
I think you have to set the min-height property of the RadDockZone to the cell height and turn the "FitDocks" property of the RadDockZone off.
I think you get a long way with those 2 minor changes. Let me know how it goes. Tomorrow I have a dev-pc on site and I can try some things for you. Didn't want to keep you waiting that long :), please try this in the mean time and let me know how it goes.