I've had this problem for 20 years and I did pack fiberglass. But the Area is so hard to get to without tearing the tile off the shower cieling. The fiberglass did not get the faraway pipes thus isolating them from any heat.
I may be able to get to the outside walls by drilling a hole in the kitchen floor above and maybe in a cabinet, where it would not be noticed. thats why foam is attractive.
I'm afraid that the foam will not travel far enough before it expands and stops. Do you know of a more fluid high pressure product?
I don't where you live with just answer's limited info on you so it would be hard for me to recommend a contractor or just just one product over another. I my self like options
HVAC Technician
35 years experience, HVAC