Hi Server,
Here's a very basic solution for your urgent matter only.
Needs a lot of improvement though !!
\version "2.18.2"
\score {
{
\time 9/8
\key f\major %% <= or whatever
r4 fis''
}
\layout {
\context {
\Score
\override KeySignature.stencil =
#(lambda (grob) (grob-interpret-markup grob
#{ \markup
\raise #1
\column { \teeny "2" \vspace #-.7 \musicglyph #"accidentals.flat" } #}))
\override Accidental.stencil =
#(lambda (grob) (grob-interpret-markup grob
#{
\markup
\raise #1.5
\column { \teeny "3" \vspace #-.5 \musicglyph #"accidentals.sharp" }
#}))
}
}
}