In my system, I recirculate PBW through all the hoses, pump, CFC and aeration fitting after each use. I remove the hose from the regulator to allow the liquid to flow into the stone.
I then rinse the system, thoroughly. Before each use, I rinse again and run Sani-Clean through the system, without the aeration fitting in place. I usually end up soaking the entire fitting in Sani-Clean. This does allow the sanitizer to soak into the stone.
Sani-Clean is also an acid sanitizer similar to StarSan but without all the foam. this does work a bit better for recirculation sanitizing. Beer stone (Calcium Oxalate), which is inorganic, is what tends to clog the pores in a stone. An acid is needed to dissolve beer stone.
I would not suggest using steam in a home brewing system. The high temperatures just might melt certain plastics. If you built the aeration fitting using the same parts as I did, the sight glass is not rated for temps above 140F.
There are also certain bacteria that can survive high temps. There are not any I am aware of that can survive an Acid Anionic sanitizer.
As far as not allowing any of the sanitizer into the fermenter, I usually allow the beer to push through any sanitizer before I connect the hose to my fermenter. I also turn on the O2 before wort starts to flow. This will blow out any liquid that may be in the O2 line.