In another part of the composition mentioned here, I want to use the sostenuto pedal:
How can I notate this?
If this is an American made piano, the notation S.P. is possible (Sostenuto Pedal).
On some Eurpoean pianos, this effect is achieved by a half-pedal technique. One depresses the notes to be held and then depresses the right (damper) pedal halfway down.