This is not a particularly elegant answer, but it may serve your purposes.
You can use the maven-dependency-plugin to output the classpath to a file. The build-classpath is the relevant goal. the configuration below will output Maven's classpath to [project directory]/target/.mavenClasspath
You could write a small script or ant task to read the .mavenClasspath file contents and append the entries to the Eclipse .classpath. If you make the script a bit smarter and remove previous entries, then set it up as an external builder, you have a nearly integrated solution.
<plugin>
  <groupId>org.apache.maven.plugins</groupId>
  <artifactId>maven-dependency-plugin</artifactId>
  <executions>
    <execution>
      <id>output-classpath</id>
      <phase>package</phase>
      <goals>
        <goal>build-classpath</goal>
      </goals>
      <configuration>
        <outputFile>${project.build.directory}.mavenClasspath</outputFile>
      </configuration>
    </execution>
  </executions>
</plugin>