I am kind of in a similar situation, but have the advantage that I studied 3D but gravitated towards compositing. However, I studied max and am moving over to maya. It is definitely quicker for me to pick it up though as I have a pretty solid understanding of the concepts and techniques.
Also, being a comper, you would have some knowledge of the pipeline and what kind of things you might need to know. As was mentioned above, especially on CG animated films, lighting and comp seem to go together a lot of the time. That is, a lighter will comp his shots, so if you can show you are a decent lighter and can comp and paintfix your own stuff to a high level, you will certainly be more employable.