I worked a bit on my Groovy Validator project.
I was trying to process the annotation in a class referenced by GroovyASTTransformationClass. I thought that there were a couple of ways it could be done, but none of them seemed to work. I was actually able to create the setter in the class, I inserted a static initializer that called my current annotation transformer that works at runtime, but neither seemed to work.
I plan on moving on to other things for the time being. I might ask for some help on the Groovy mailing list, but if I do, I will have to formulate a coherent request. I asked for help on the list a while back, and I think I included too much detail because I never got a response.