I would suggest doing a drop leg solution for your knife to get it out of the way of the hip belt.

While attaching it to the shoulder strap would work and would keep the knife near you while you had the backpack on, once you remove the pack you don't have the knife.

From my old SAR days, the philosophy was that if you didn't have it ON you, you didn't really have it. That type and style knife is a great tool one that I would rather have on my body than have to say "where is my pack" when I need it. Speaking of "where is my pack" if you take off your bag and it decides to go on "walk about" down a hill/ into a river or anything like that, well you get the picture.

Aside from all of that I would use Electrical tape to attach the knife to my shoulder strap. Just be VERY careful when you put the knife back in the sheath..