Paul,
If I'm understanding your question correctly, there is no way I know of to "structurally" define a Fine ending (i.e., to where you could "unfold it" automatically like with volta repeats). All the documentation I've seen says you "cosmetically" define it using rehearsal marks and a bit of tweaking.
This is the snippet given for the "D.C/S al Fine" direction:
\relative c'' {
g2 c
d,2 a'
\once \override Score.RehearsalMark.break-visibility = #end-of-line-visible
\once \override Score.RehearsalMark.self-alignment-X = #RIGHT
\mark "D.C. al Fine"
\break
g2 b,
c1 \bar "||"
Cheers,
Carl