It sounds like CUSE grants are expected to be interdisciplinary. My project is strongly disciplinary and does not lend itself to an interdisciplinary approach. May I still apply for a CUSE grant?

Yes, you can apply for a research CUSE grant as the only PI. While the CUSE grants program promotes interdisciplinary collaboration, applications from disciplinary research areas with great potential to further scholarship, or that may lead to extramural funding opportunities are also encouraged.