An (ugly) workaround is to specify the ivy pattern for the repository, pointing to a server that will return a 404 instead of a 403.
buildscript {
repositories {
ivy {
ivyPattern 'http://google.com/FAKE_URL/not_a_real_file.txt'
artifactPattern 'http://cloud.github.com/downloads/[organisation]/[module]/[module]-[revision].[ext]'
}
}
dependencies {
classpath 'bmuschko:gradle-izpack-plugin:0.1'
}
}