It is not possible out of the box. But you could prepare your POM for that:
<project ...>
...
<properties>
<buildDirectory>${project.basedir}/target</buildDirectory>
</properties>
...
<build>
<directory>${buildDirectory}</directory>
</build>
...
</project>
If you now do a simple mvn package
it will behave as default: putting the output into the project's target directory.
But you also now can run a
mvn package -DbuildDirectory=<any other directory>
and all output is done to the new place. Note, that I said: all output! It is not only the artifact (the JAR or the WAR), but all compiled classes, the surefire reports, and so on.