If I need a completely customized interface including differently shaped "controls" etc, I usually work with clickable regions and where applicable just images.
May not be as comfortable as real UI controls, but is very easy to program and gives you ultimate freedom.
I do use text input controls, though, usually set to borderless, if I need them. Borders and decoration come from the background image(s).
Most of the user interfaces for my VST audio plugins are written that way.