I know that there is a line that can be written, as the pedal line, but indicating it is the sostenuto pedal. But I have found other scores that seem to call -or could be played with- the sostenuto pedal, without writting the lines. And I was asking myself if that is allowed. Also, if it is allowed, what is the best way to write it. In example, I have these two scores, that have the notes as indicating different instructions for two instruments -as in violins pentagram in an orchestral score-.
Mussorgsky, Bilder einer Ausstellung, Promenade:
Bach, Praeludium I, BMV 846
A