GMaven -

gistfile1.xml

<plugin>
	<groupId>org.codehaus.groovy.maven</groupId>
	<artifactId>gmaven-plugin</artifactId>
	<executions>
		<execution>
			<phase>generate-sources</phase>
			<goals>
				<goal>execute</goal>
			</goals>
			
			<configuration>
				<source>
				public void replace(srcExp,replaceText){
					def currentDir = new File(project.basedir,"src/main/java");

					def fileText;

					//Replace the contents of the list below with the
					//extensions to search for
					def exts = ["WebMethodResult.java"]

					currentDir.eachFileRecurse({file ->
					for (ext in exts){
						if (file.name.endsWith(ext)) {
							fileText = file.text;
							fileText = fileText.replaceAll(srcExp, replaceText)
							file.write(fileText);
						 }
					 }
					})										
				}

				replace("public class WebMethodResult \\{","public class WebMethodResult implements IWebMethodResult \\{");
				</source>
			</configuration>
		</execution>
	</executions>
</plugin>