Une réponse tardive... et une solution peut-être un peu trop simpliste...
\version "2.20.0"
%% markup defs:
#(define-markup-command (croc layout props arg txt) (number? markup?)
(interpret-markup layout props
(markup
(#:right-align
(#:center-column (
(#:path 0.2 `((moveto 0 0)(lineto 0 -.5)(rlineto ,arg 0)(rlineto 0 .5)))
(#:bold txt)))))))
%% Test:
\include "
makam.ly"
\fixed c' {
\cadenzaOn
\omit Stem
\override TextScript.Y-offset = #-4
\override TextScript.X-offset = #.5
c2
d4*2-\markup\croc #3.6 "1"
efb -\markup\croc #3.6 "¾"
f -\markup\croc #3.6 "¾"
g2-\markup\croc #3.6 "1"
}