Personally I would say your options are:

• Learn Java ;-)
• Go find out from the client why they are using j2ee. It may not be for a good reason or set in stone. Maybe perl would be a more appropriate solution for that particular problem. In which case you can get the requirements changed.
• Equally, there might be a good reason for them to use j2ee. Maybe the rest of their code is Java. Maybe their internal developers are all Java coders. In which case using perl would just be counterproductive.

In my experience you should either stick to client requirements, get the client to change them, or tell the client to get another contracter. Finagling around requirements tends to produce lawyers at inconvenient times ;-)