Software Engineering in general is a very creative process, especially in the early stages of development like requirements engineering or architectural design where sketching techniques are used to manifest ideas and share thoughts. On the one hand, a lot of diagram tools with sophisticated editing features exist, aiming to support the engineers for this task. On the other hand, research has shown that most formal tools limit designer's creativity by restricting input to valid data. This raises the need for combining the flexibility of sketch-based input with the power of formal tools. With an increasing amount of available touch-enabled input devices, plenty of tools supporting these and similar features were created but either they require the developer to use a special diagram editor generation framework or have very limited extension capabilities. In this paper we propose Scribble: A generic, extensible framework which brings sketching functionality to any new or existing GEF based diagram editor in the Eclipse ecosystem. Sketch features can be dynamically injected and used without writing a single line of code. We designed Scribble to be open for new shape recognition algorithms and to provide a great degree of user control. We successfully tested Scribble in three diagram tools, each having a different level of complexity.