Gotta say, this question and the process explained threw me for a loop.
You have a network print server where it’s advertising an available printer, but instead of the native printer system on a client device, you want to NOT use the CUPS server to print? That’s what it’s there for. I’m confused on why you have it then.
If your goal is just to have clients print as directly as possible to a printer…you already have that with CUPS running. I guess I’m not getting why submitting via web form is useful in this case.