You can use any LiveCD-type Windows or Linux OS on USB drive. Just boot from it and do whatever you want. This is the easiest way. You can try using Total Commander, worked fine on my work PC. I don’t know how, but I was able to transfer files from PC to USB.
Dual booting seems to be the only way for now. I tried the Total Commander but it gets blocked all the same. Still hoping this is possible like you can load samples to SP404 via the app. Booting from external drives would be just a pain to go through every time