A bit of a plug but I wrote a primitive and ugly script that attempts to embed msg definitions in .bags after they have been recorded. For the limited time I was required to use rosjava this allowed me to still use rosbag.
Surely one of many implementations of something similar, but: rosbag_fixer.
Edit:
Not sure what the status of it is, but I came across ernestmc/rosjava_actionlib while looking into that.