F-Modifier Goodies (as requested by @ndy):

* Copy/Paste operators for F-Modifiers
Available in Graph and NLA Editors. Use the Copy/Paste buttons beside the 'Add Modifier' buttons.

Copy copies all the modifiers of the ACTIVE F-Curve or Strip depending on the editor.
Paste pastes modifiers from the buffer to all the selected F-Curves or Strips, adding the new modifiers to the ends of each list.

* 'Stepped Interpolation' F-Modifier
This modifier holds each interpolated value from the F-Curve for several frames without changing the timing. 

This allows to preview motions 'on-twos' for example without altering the timing, or having to go through setting heaps of keyframes. In this case, Andy wanted to use this for CG <-> StopMo.

source/blender/editors/include/ED_anim_api.h

@@ -452,9 +452,28 @@ void ANIM_draw_previewrange(const struct bContext *C, struct View2D *v2d);
 /* ************************************************* */
 /* F-MODIFIER TOOLS */
 
+/* ------------- UI Panel Drawing -------------- */
+
 /* draw a given F-Modifier for some layout/UI-Block */
 void ANIM_uiTemplate_fmodifier_draw(struct uiLayout *layout, struct ID *id, ListBase *modifiers, struct FModifier *fcm);
 
+/* ------------- Copy/Paste Buffer -------------- */
+
+
+/* free the copy/paste buffer */
+void free_fmodifiers_copybuf(void);
+
+/* copy the given F-Modifiers to the buffer, returning whether anything was copied or not
+ * assuming that the buffer has been cleared already with free_fmodifiers_copybuf()
+ *	- active: only copy the active modifier
+ */
+short ANIM_fmodifiers_copy_to_buf(ListBase *modifiers, short active);
+
+/* 'Paste' the F-Modifier(s) from the buffer to the specified list 
+ *	- replace: free all the existing modifiers to leave only the pasted ones 
+ */
+short ANIM_fmodifiers_paste_from_buf(ListBase *modifiers, short replace);
+
 /* ************************************************* */
 /* ASSORTED TOOLS */