Model-Driven Web Engineering (MDWE) methodologies have proven to be a mature way of developing web applications, dramatically increasing productivity during development. However, after more than a decade of evolution, the artifacts and processes used to gather requirements have not changed substantially. At the same time, the capacity of quickly adapting to emergent domain-specific requirements (a feature that became popular with the massive adoption of agile approaches) has become hard to achieve in these methodologies. In this context, in order to implement this kind of refined requirements as fast as possible, changes are usually applied directly to the generated application, losing the abstraction and its inherent productivity provided by the Model-Driven process. Another way of implementing this kind of changes is by extending the modeling language, but this implies a high effort and, again, a consequent productivity loss. In this paper we propose a model-driven development approach called MockRE that captures requirements using User Interface prototypes (mockups) that end-users can understand completely. The process and tooling presented here allows end-users to express requirements annotating the mockups with textual descriptions, and also generating a running application in the same way that MDWE environments do. Developers may later use these initial specifications placed by end-users as valuable model concepts that can be refined through direct coding in a non-intrusive way. Through this strategy, MockRE intends to make a more extensive reuse of end-users specifications throughout the whole developing process.