I'd say look and see if the internal PC has some kind of vga/hdmi output. That's liable to be your best bet if you can get into the internals of the linux pc itself. All in all, those type of devices are very limited in what you can do outside of their specifications, and doing so voids the warranty and risks breaking the device.
IMO, those devices are completely pointless. Just install gauge software on your carpc, buy an ELM327 based device and presto, gauges on as large of a screen as you would like.