The dynamic master automatically includes all projects on the same level as subprojects. For this example gradlew projects produces this:
Root project 'master'
+--- Project ':project_a'
+--- Project ':project_b'
+--- Project ':project_c'
+--- Project ':project_d'
\--- Project ':project_e'
If you now decide to remove or add another project you have to add -PrefreshProjects to your Gradle command to trigger a refresh.