Andrew Eisenberg was kicking off a rebuild of the jars for that yesterday, should be available imminently. Not sure if he will build a new version or switch to a snapshot model - I guess either way you will have to slightly edit your pom to pick it up. Look out for the announce. That build does include something else I was temporarily working on (but have now backed out) - so I hope that change doesn't disturb compilation for you. If you see problems about things being unresolved, let me know. It will also be groovy 1.7.5 level.
What prevents this working is the lack of a defining project when setting up the groovy parser with the appropriate groovy class loader for transforms. With no project it doesn't discover the projects classpath and that classpath is what is used to populate the GroovyClassLoader that will be searched for transforms. We just have to add the extra logic in to cope with the batch case and retrieve the path from the FileSystem in the LookupEnvironment.