Use cable ties and manage the cables, using the cable anchors in the case's designed motherboard tray. Cable ties are your friends here and planning ahead where the cables will go helps the same as the anchors and the cable ties.
^ I did that build for a friend of mine, took me a couple of days to get the cables the way I wanted them. That was about 5 years ago, now it takes me less to manage cables, though the key factor here is you need time to manage said cables. Managing them to be worthy enough to show to people.