Underlined + double underlined fingering instructions for accordion scores

[Ledocq-Boccart]

Hello!

For left hand keyboard of accordion, fingering instructions are annoted
with figures as 2,3,4,5 for the middle button row; with simple
underlined figures (2, 3, 4, 5),  the following row , and
double-underlined figures for the last bass button row (I caanot give
example with the font of the editor of my e-mail text processor).

I tried with
c^ \markup { \underline 2 }
in a score, for example, but without succes (I did not find any
\underline instruction.in the doc)

Does this topics have already been solved by Lilyponders?
How can it be solved?

Thank you for answering.

Charlie