Word completion interfaces are ubiquitously available in mobile virtual keyboards; however, there is no prior research on how to design these interfaces for screen reader users. In addressing this, we propose a design space for nonvisual representation of word completions. The design space covers seven categories aiming to identify challenges and opportunities for interaction design in an unexplored research topic. It is intended to guide the design of novel interaction techniques, serving as a framework for researchers and practitioners working on nonvisual word completion. To demonstrate its potential, we engaged blind users in an exploration of the design space, to create their own bespoke word completion solutions. Through this study we found that users create alternative interfaces that extended current screen readers' capabilities. Resulting interfaces are less conservative than mainstream solutions on notification frequency and cardinality. Customization decisions were based on perceived benefits/costs and varied depending on multiple factors such as users' perceived prediction accuracy, potential keystroke gains, and situational restrictions.