That is the direction I have to go when I go ATG on my neck. It isn't easy at all, and has taken a lot of experimenting to get BBS on my neck.

All I can say is try your best to stretch your skin in a way that lifts the hairs up, and use a smooth (but lightly held to prevent knicks) stroke. Turning and tilting my head as much as I could while still being able to see helped as well. I also use grip 9 and 10 from this page.

That is what works for me. It may not work for you though, as we likely have different growth patterns. Experimenting on your own with different grips and strokes is the only way you will find the best approach for you. It took me 3-4 months of experimenting (and not getting great shaves) before I finally was able to get BBS on my neck.