There are many known limitations to using ControlAddIn at moment. Some are inherent to IFrames and might be solved by HTML5 Web Components (once legacy browsers are no longer supported), but others are to do with the management of CSS and DIV components, combined with Z-Index. There are times when we do want to pop-up a ControlAddIn and layer it over the screen, rather than take up space. As far as I can see this is not supported at the moment.