I think this ticket is invalid.
1: It doesn't matter that Ivy or now Maven (due to
AVRO-647) downloads various jars to build, does it? Is the policy "no bundled dependencies" for the eventual artifacts? The output of the build has no bundled artifacts, other than avro-tools.jar which we currently do bundle all dependencies in it.
2: If there is a way to do this with maven, its part of maven. There are hundreds of other java projects that use Maven , Gentoo must have some sort of policy for working with projects that build with and generate maven artifacts.
I am going to close this ticket, but feel free to re-open it if there is a requirement to change the build after