I remember Rob mentioned plug-in in our lab component which has similar functionality and provides source lookup for *.src.zip files in selected for lookup folder. It can be adjusted to look inside *.jar files and after that we can handle looking into source archives inside selected source archive or file system. How, just by adding two types of source lookups: Eclipse's one for sources in external folder and our new one for archives in file system or archives inside archive. Considering all above it looks doable for me