Avro IDL: custom logical type implementation

How can I implement custom logical type supported by Avro IDL? The main problem with generated by Avro entities is need of custom converter methods to mapping business entities to/from Avro entities. E.g. I need to convert Avro's UUID (fixed UUID(16)) to Java's java.util.UUID and back. Ideally, I want implicit conversions, but in reality, a possibility of Avro IDL compiler configuration to produce specific Java-based API would be the best solution.