placement sostenuto

[luis jure]

hello list, i'm here again after a long time without using lilypond
(meaning that i'm already forgetting the little i ever managed to learn
about it...)

i'm using the sostenuto sign (c--), but for my taste the default placement
is too close to the head of the note. i'm trying to include a global
override in my score to separate it a little bit from the note, but i can't
find the appropriate syntax. any pointers would be greatly appreciated.

best,

lj