The build process is documented up to a certain point:
How to build SNAP from sources
How to run and debug SNAP from an IDE (IntelliJ IDEA)
With both information, it is possible to gather all the build out in a directory and add a batch or shell script which follows the configuration settings specified for IntelliJ IDEA.
But this is not straight forward.
Without the installer, it is difficult to build it. But maybe you have or can obtain a license for Install4j. If so, you only need the snap-installer project use the snap.install4j file.