I initially also thought of using HIPS and PVA (I have some and tried it) with the dual extruders.
Those soluble materials are great for hard to remove or internal supports, although in general are a real pain to print. And HIPS - dissolving that stuff is sticky, smelly and not pleasant.
For break-away supports I got the idea from this youtube video: Using PETG as Support Material for 3D Printing PLA - YouTube
I was very pleased with how well it works for break-away supports. So much so, that I am now looking for other material combinations that will provide that same amount of adhesion yet separation for higher temperature materials.