not sure about hard mode when they run faster but before you could do it without any skills if you practiced. It was pretty much the same as setting off traps.
some times, they all go for the same spirit, and the suicide skill get interupted, as the spirit dies .. so its got to recharge, just run up the hill a bit, send ur pet in.
btw, it goes faster if you place the spirits a little lower (just after entering weakness zone), in a triangle next to a wall, then simply stand in the triangle.