I experimented with creating my own tool for building j2me projects from source (since plugins are no longer being developed). I wrote my own simplified config for the description of the application and the MIDlets in it for this tool. Burp collects manifests and jars itself.

To build j2me, burp uses openjdk8, no other wtk/sdk needs to be installed. In the future, it would be nice to wrap this in the build stage for GitHub, then j2me projects will be built right there. It does not yet support code obfuscation (i.e. the jar is large and easy to decompile), but the required minimal libraries cldc/midp, burp carry with it itself.