I suggest that this information be put in FAQ 145: I am using S2. Why are some customization options not available? or at the top of FAQ 171: Which options are currently supported by each public S2 layout?.
This is assuming that none of the S2 styles support special comment page layouts for free users...which I believe is the case. Feel free to speak up if I'm wrong, though. I'm definitely not an S2 expert. :)