How do I use "drush make" modules with a local module code?
You can set up local domains and local git repositories or tarballs like so:

projects[my_module][type] = "module"
projects[my_module][download][type] = "file"
projects[my_module][download][url] = "http://localhost/my_module.tgz"
projects[my_module][subdir] = "contrib"


Then in your build script you could just recreate the tgz