Unfortunately, I'm unable to determine what type of compression algorithm is being used on the remote files. Unless a developer @lazypenguin is willing to chime in and point us in the right direction then we can make our own custom launcher.
Or even better, some insight on what windows system call is being made to perform downloading of the remote manifest, because this is where it currently fails under Wine, as noted above. I've tried both wininet and winhttp libraries w/ urlmon and it fails, so I'm not too sure at the moment and don't have the time to debug it further.