First step is to fix the horizontal alignment, using
indent = 0 and ragged-right = ##t (if you keep the Staff symbol
engraver, you will realize why).
For the vertical alignment, there's a markup command
\vcenter to set the alignment point on a specific markup
to be centered. There are no similar markup commands for
top and bottom aligned, but there you can use \general-align.
The following modified version of your example is hopefully
fairly close to what you want:
\markup { \general-align #Y #DOWN "per il clarinetto" \general-
align #Y #DOWN \score {\new Staff \with {
\remove "Time_signature_engraver"
\remove "Clef_engraver" \remove "Staff_symbol_engraver"
} {
d'4:32
} \layout { ragged-right = ##t indent = 0} } }
Note that I changed the pitch of the note. Apparently, the
stave still allocates some space even though it's not printed.
%%%%%%%%%%%%%%%%%%%%%%
\markup {{\musicglyph #"scripts.prallprall" }"= vibrato ampio"}
Here, you can use
\markup {{\musicglyph #"scripts.prallprall" } \vcenter "= vibrato
ampio"}
/Mats