\header { tagline = ##f }

ossia =
#(define-music-function
  (music ossia-music) (ly:music? ly:music?)
  (let ((name "initialized"))
    #{
      \applyContext
      #(lambda (context)
         (set! name (ly:context-id (ly:context-find context 'Staff)))
         )

      << \new Staff \with {
        #(ly:make-context-mod
          `((apply ,(lambda (c)
                       (set! (ly:context-property c 'alignAboveContext)
name)
                     ))))
     \remove "Time_signature_engraver"
    \magnifyStaff #2/3
    \hide Clef
    firstClef = ##f
         } { #ossia-music }
      #music
      >>
      % Create \new Staff with ossia-music
    #}))

%% Apologies that I can't present this with the arguments in a
%% more sensible order, which would allow commenting just one line

\new Staff = "foo" \relative {
  c'4 f b e
  \ossia
  { a^"main" f d b }
  \relative { f''^"ossia" c g d }
 f g a2
}

\new Staff = "foo" \relative {
  c'4 f b e
  %%\ossia
  { a^"main" f d b }
  %%\relative { f''^"ossia" c g d }
 f g a2
}

\new Staff = "foo" \relative {
  c'4 f b e
  a^"main" f d b
 f g a2
}