We seek to make physical user interface (PHUI) design more like graphical user interface (GUI) design by using a drag-and drop interface to place widgets, allowing widgets to be repositioned and by hiding implementation details. PHUIs are interfaces built from tangible widgets arranged on the surfaces of physical objects. PHUI layout will become more important as we move from rectangular screens to purpose-built interactive devices. Approaches to PHUI layout based on sculpture make it difficult to reposition widgets, and software approaches do not involve placing widgets on the device exterior. We created PHUI-kit, a software approach to PHUI layout on 3D printed enclosures, which has a drag-and-drop interface, supports repositioning of widgets, and hides implementation details. We describe algorithms for placing widgets on curved surfaces, modifying the enclosure geometry, and routing wiring inside the enclosure. The tool is easy to use and supports a wide range of design possibilities.