Yeah ..sanitation seems to be the bugaboo and who wants to find out several weeks or months down the road that your cheese is now inflating....
I think if I were to use a coil type immersion chiller, then I'd make one with as few nooks and crannies as possible, e.g. lose the copper wire ties that everyone seems to use on these so there's nothing but smooth copper pipe in the milk ...and then I'd use steaming to sanitize. I think a large pot with a couple of inches of water in it might work. Wipe the chiller down with a strong chlorine mixture, rinse, then steam in the pot for 20 minutes or so ...make a foil lid that can be 'fit' around the copper tubes where they come out over the top of the pot. With beer brewing, you get sanitization for free by putting the chiller into the boiling wort around the time you add your late hops. When done chilling, rinse in cold water, wash, then wipe down with chlorine and rinse. Might work.
Brian