Have just posted an update to our j2k plug-in for Photoshop and After Effects. The main change is the addition of a "Digital Cinema" option when saving files. This will make JPEG 2000 files compatible with the DCI specification. From there you can use a tool like OpenDCP to finish the process of creating an MXF file ready for digital projection.
Also new is a real PDF manual. Of course, the plug-in is still free. Enjoy!