Spend three months working closely with an open source community. Bring your technical writing expertise to the project's documentation. Learn about open source and new technologies. Add more skills to your resume.
Invite an experienced technical writer to work on your documentation for three months. Provide some project ideas based on your documentation needs, then work with a technical writer to build your doc set, improve your information architecture, or develop a much-needed tutorial.
Introduce a technical writer to your open source project and community. Help the technical writer use the project's tools and understand the product. Contribute together to some shiny new docs that enhance your community and your code.