NetLoaderZ is based upon ry755's NetLoader and lets you upload Uzebox roms via the UART header using the ZModem protocol.
Copy default/netload.bin into the root of your Uzebox SD card.
Connect your computer to your Uzebox via the UART headers.
Run NetLoaderZ on your Uzebox.
Run a ZModem program (eg minicom under Linux) to transfer a .uze rom to your Uzebox.