replace a notehead with a centered text

[Paolo Prete]

Hello,

how can I replace a notehead with "some text" centered on the stem?

If I use:

customNotehead  = {

\once \override NoteHead.stencil = #ly:text-interface::print

  \once \override NoteHead.text = \markup {  \fontsize #6 "some text" }

}

the notehead is always at the left or at the right of its stem...

thank you

P