Best way to cull as dual totem?

If you want to self cast it, I think Arc + IIR + Culling Strike would work best since it seems pretty easy to hit several at a time with it. I use Arc with Curse on Hit to apply curses in my Dual Totem build and it works pretty well.

Since you can have 2 totems active, another option would be to put the cull and IIR on a Flame Totem. When the monsters get close to 10%, replace one of the Shockwave totem with the flame totem. It hits very fast so it will cull as soon as the monster hits the threshold.