This extends romaintaz's answer, which is awesome in that solves the problem and also clearly points out maven's missing functionality. I picked up a later version of the plugin, and added the case where the project could be more than 3 levels deep.
<pluginManagement>
<plugins>
..
<plugin>
<groupId>org.codehaus.gmaven</groupId>
<artifactId>groovy-maven-plugin</artifactId>
<version>2.0</version>
</plugin>
..
</plugins>
</pluginManagement>
I elected not to use a property to define the filename. Note if the build.properties is not found this will spin forever. I added a .git dir detection, but didn't want to over complicate the response so it's not shown here.
<plugin>
<groupId>org.codehaus.gmaven</groupId>
<artifactId>groovy-maven-plugin</artifactId>
<executions>
<execution>
<phase>validate</phase>
<goals>
<goal>execute</goal>
</goals>
<configuration>
<source>
import java.io.File;
String p = "build.properties";
while(true) {
File f = new File(p);
if(f.exists()) {
project.properties['project-properties-file'] = f.getAbsolutePath();
break;
}
else {
p = "../${p}";
}
}
</source>
</configuration>
</execution>
</executions>
</plugin>