Nikon D3s back button focus

Hi
Just acquired a D3s to use with my D500 help save in the amount of shutter activations for sport. My D810 is good for sport but FPS is not quite fast enough for photographing hockey. The D3s is fast enough, I like to use back button focusing but noticed the back button focuses but the VR wont come on until I press the shutter down halfway. Ive tried a few things to use back button and VR come on without pressing shutter halfway down cant work it out. Can anyone advise how it can be changed please.
Thanks
Just acquired a D3s to use with my D500 help save in the amount of shutter activations for sport. My D810 is good for sport but FPS is not quite fast enough for photographing hockey. The D3s is fast enough, I like to use back button focusing but noticed the back button focuses but the VR wont come on until I press the shutter down halfway. Ive tried a few things to use back button and VR come on without pressing shutter halfway down cant work it out. Can anyone advise how it can be changed please.
Thanks

I cannot answer your question but the following observations might help. My D700, which is based on the D3, has a dedicated AF-ON button and when I use it the VR does not activate. However my D750 does not have a dedicated AF-ON button so I have assigned the back button focus to the AE-L/AF-L button. When I use that as back button focus both the A/F and VR jump into life. It appears to vary between Nikon models.