As far as I am concerned, this is always a matter to be discussed in pregame. When I am the R, I will pregame that the T always brings in the subs. This will, of course, require that the partners have good communication (voices, eyes, whatever).
I have yelled, from L, to my partner, at T, that there were subs at the table. I don't think there is anything wrong with this and it is smoother to have the same positioned ref bring them all in.