...Google finally released an uploader designed just for Linux.
The uploader essentially works just like the Windows version, with one small tweak: OGG support. OGG files will automatically be transcoded to 320kbps MP3 files, which will inevitably make the already painfully slow uploading process last even longer -- but hey, at least you can finally use that beta invite, right?
To grab the uploader, head over to the Google Music Landing page, hit 'Download the Music Manager', select the appropriate package based on your Linux distro, and install.