HP Z640 Headless?

I have an HP Z640 workstation that I have pressed into service as a proxmox host. I am not doing GPU pass through and would love to be able to run this without the included Nvidia Quadro card that it came with, just to lower the idle power draw and free up a PCIe slot. Unfortunately, the bios won’t post when the GPU is removed. The system gives an error beep, displays the red LED power button (an error message) and then shuts down. If I re-install the GPU all returns to normal. Is there a hack or a workaround to enable this machine to run headless?

Maybe check the bios and see if you have any primary display configured and set it to none or integrated gpu (even if the cpu doesn’t have one).