I have a Jenkins cluster that is shared by several teams, that I can configure build jobs on, However i can\'t easily make changes to the Jenkins configuration itself.
If your company is using Nexus Pro (as you've already mentioned), then your unique Maven settings.xml can be stored there, and retrieved at build time using the nexus-maven-plugin as described here: http://books.sonatype.com/nexus-book/reference/maven-settings.html
Combined with token-based access (again, Nexus Pro does this), you do not need to store passwords insecurely in the settings.xml (see https://books.sonatype.com/nexus-book/reference/usertoken.html)