You could try using a cheap card that has only 8 or 4 lanes and see if it boots, or isolate the last 8 lanes on your gpu with some tape. But you can also go ahaed and order the splitter. Ebay steals 10% ... thats why they cheaper in my shop. My preference would be to bifurcate at the mainboard and use 2 cables from there. This may however only work with one of the bigger tops on this case. Not sure about the clearance there... Use this one: https://peine-braun.net/shop/index.php?route=product/product&path=65_59&product_id=68 If you have a better idea let me know, and I will make a custom one for you. Custom ones are more expensive though as I have to pay around €100 for the PCBs alone, add the hours of designing the PCB.