Maven issue with buildnumber:hgchangeset properties not propagating to children - maven

Question

I have a multi-module project which uses the buildnumber:hgchangeset plugin to generate changeSet and changeSetDate properties, which then get blatted out into the manifest for each module, like so:
pom.xml (parent):
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>buildnumber-maven-plugin</artifactId>
<version>1.0</version>
<executions>
<execution>
<phase>validate</phase>
<goals>
<goal>hgchangeset</goal>
</goals>
</execution>
</executions>
</plugin>
...
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-jar-plugin</artifactId>
<configuration>
<archive>
<manifestEntries>
<ProjectVestion>${project.version}</ProjectVestion>
<ChangeSet>${changeSet}</ChangeSet>
<ChangeSetDate>${changeSetDate}</ChangeSetDate>
</manifestEntries>
</archive>
</configuration>
</plugin>
After a bit of experimentation, I discovered that having buildnumber:hgchangeset execute for each module contributed a significant amount of time to the overall build time, presumably because it's forking hg.exe every time it needs to get the changeset ID of the local repo.
I then thought it would be a good idea to set the inherited property to false on the buildnumber plugin, in order to only have it run once for the parent. Unfortunantly, doing this causes the changeSet and changeSetDate properties to not be "visible" to the child modules.
My question is: is it possible to set things up in such a way that buildnumber:hgchangeset runs only once, but the properties that it sets become visible to children modules?
I suppose alternatively I could write things out to a property file, and have each module read it back in, but this does not seem like idiomatic Maven to me.
Thanks in advance,