This is probably not a permanent solution, the byte code generation should probably happen within the 'Java' layer and it probably shouldn't be dependent on cglib. However, for those of you that are interested I created simple implementation that allows users to implement a abstract class from within JRuby. I pasted a link to the code and a link to some examples.
Implementation: http://pastie.caboo.se/151677<http://pastie.caboo.se/151677> Examples: http://pastie.caboo.se/151695 <http://pastie.caboo.se/151695> Note: cglib must be in the classpath
