I can tell you how I did it, I'd be interested to see if someone else has a better way.
I was working with Windows, so not knowing your OS you might have to modify. I created a new printer on the computer attached to the label printer. I selected the USB port but used Generic manufacturer and Generic / Text Only driver. Thus windows would not try to reformat or alter the raw text I send. I then shared the printer on that machine with the name Zprint.
My XoJo program from that point was fairly straight forward. I used the file name "\\127.0.0.1\Zprint" in a new FolderItem. Created a TextOutputStream using that FolderItem and output my text file directly with ".Write", flushed the buffers with ".Flush" and then closed the TextOutputStream.
I've done this with both EPL and ZPL language printers, on both Windows XP and Windows 10 machines.