include another song without outputting anything

all_base_includes.ly

@@ -29,6 +29,7 @@
 \include "swing_style.ly"
 \include "inline_score.ly"
 \include "custom_indentation.ily"
+\include "include_from_song.ily"
 
 % reset important variables
 LAYOUT = \layout { \generalLayout }

include_from_song.ily

@@ -0,0 +1,7 @@
+includeFromSong =
+#(define-void-function (filename) (string?)
+  (let ((noDefaultOutputBackup noDefaultOutput))
+    (set! noDefaultOutput #t)
+    (ly:parser-parse-string (ly:parser-clone)
+      (ly:format "\\include \"~a\"" filename))
+    (set! noDefaultOutput noDefaultOutputBackup)))