Modding a PCIe 8 pin out of HP Prodesk G9 SFF motherboard

[M.Reza]

My HP ProDesk 400 G9 SFF has a 6-pin power output (P160 SATA Power) on its motherboard to deliver power to HDDs and other SATA devices. I wanted to know if it's possible to use this socket, with some modding, to deliver power to a discrete GPU. The power supply is rated for 240W, and the CPU is rated at 65W. I believe there is plenty left that could be used to operate a 100-120W GPU.

I've come across SATA cables to PCIe 6-8 pins online, but I'm wondering why not utilize the pinout on the motherboard directly instead of adding a potential weak link in the middle?

I'm aware that SATA power is rated to deliver 54W, and this board has 2 SATA ports, plus one that isn't soldered (the 600 variants have it soldered) so theoretically, it should be able to output at least 54W x 2 = 108W

I haven't verified the pinout voltage with a multimeter yet, but since it's SATA and the cable going into it is color-coded, it should have the correct voltages. My question is, can I safely wire these voltages to a PCIe 8-pin cable?

 

[SFFMunkee]

I suspect the traces to those ports on the motherboard aren't actually designed to handle 54W, let alone on 12V alone.
I'd be far more inclined to source it directly from the power supply, otherwise you'll cook the PSU, motherboard AND GPU if something goes wrong.