If I understand you correctly, you are in search of a molex -> slim sata power connector adapter. Those aren't "super long" typically. They go on Amazon for like $5. Just search "slim sata molex adapter".
Those molex-to-slimsata tend to look cheap as well as being cheap. And then you need a molex cable from your PSU, which in the 850P2 is half a meter long and has 4 ugly molex plugs.