Is this actually possible or does music transfer to a 645m require either a PC or MAC? I only have access to a Chromebook (and a security-crippled work Windows laptop that I can't install software on or copy any files to an external device) so don't have Garmin Express and copying and pasting (using Chromebook) onto the watch isn't working.
I was hoping that getting music onto the device would be easy, even without a PC.