I have just finished the first version of a Java 6 compiler plugin, that automatically generates wrappers (proxy, adapter, delegate, call it what you like) based on an annotatio
Kevin is entirely correct, but just for completeness it's worth mentioning that there is another alternative - write a compiler plugin that generates source. This is the approach that I've adopted in Borachio. It's not a very satisfactory solution, but it can be made to work.
Edit - I just reread your question and realised that you're actually asking about generating source anyway
So there is no support for this directly, but it's basically just a question of opening a file and writing the relevant "print" statements. There's no way to invoke the compiler "inside" a plugin AFAIK, but I've written an sbt plugin which hides most of the complexity of invoking the compiler twice.