How should I insulate around pipe/cable holes in drywall?
I am proceeding on the assumption that these aren't visible areas, so looks do not matter. 

I think you were right the first time, I'd use expanding foam for those jobs. I've used it in all sorts of cases like yours and it has done well. It isn't going to crush anything, even flexible dryer hose. 

The alternative would be to cut pieces of drywall with the right diameter holes and to screw and/or glue them into place around this material. You'd need to move those wires around some if you have enough slack. Once the drywall is in place you'd just use caulk or silicone on the remaining small gaps.