Integrated development environments (IDE) support developers in a variety of tasks. Unobtrusively capturing developers' cognitive load while working on different programming tasks could help optimize developers' work experience, increase their productivity, and positively impact code quality. In this paper, we propose a study in which the IntelliJ-based IDE plugin CognitIDE is used to collect, map, and visualize software developers' physiological activity data while they are working on various software development tasks. In a feasibility study, participants completed four simulated everyday working tasks of software developers - coding, debugging, code documentation, and email writing - based on Java open source code in the IDE whilst their physiological activity was recorded. Between the tasks, the participants' perceived workload was assessed. Feasibility testing showed that CognitIDE could successfully be used for data collection sessions of one hour, which was the most extended duration tested and was well-perceived by those working with it. Furthermore, the recorded physiological activity indicated higher cognitive load during working tasks compared to baseline recordings. This suggests that cognitive load can be assessed, mapped to code positions, visualized, and discussed with participants in such study setups with CognitIDE. These promising results indicate the usefulness of the plugin for diverse study workflows in a natural IDE environment.