The graphical UI-builder is a type of tool that has been implemented for many programming frameworks and programming languages, and it utilizes many useful and intuitive concepts facilitating easy UI-modeling and thus faster development of applications. In this paper we identify a problem of the separated design-view/data-view concept that is used in many GUI-builders, and we propose a solution to these problems. We present an approach that leverages visual, in-place, data flow modeling, making data flow modeling within UI-builders more efficient than in classic UI-builders and also, more efficient than in state-of-the-art presentationoriented end-user modeling approaches.