Maybe like this using make-dynamic-script:
%%
doubledyn = \markup { \normal-text \column {"1.x cresc. - - - - - - -" "2.x
decresc. - - - - - -" } }
doubledynamic = \tweak DynamicText.self-alignment-X #LEFT
#(make-dynamic-script doubledyn)
mymusic = \relative c'' {
\repeat volta 2 {
c4^\doubledynamic c c c c c c c
\alternative {
{ d d d d }
{ e e e e }
}
}
}
%%
The extender lines aren't automatic this way, you'll have to do them manually,
maybe that's good enough
