This feature is already available in CHDK-DE. You must only add some lines in the menu part.
MENU_ITEM (0x0 ,LANG_MENU_CURVE_CURRENT, MENUITEM_SEPARATOR, 0, 0 ),
MENU_ITEM (0x0 ,(int)conf.curve_file, MENUITEM_TEXT, 0, 0 ),
MENU_ITEM (0x0 ,(int)"", MENUITEM_SEPARATOR, 0, 0 ),
For LANG_MENU_CURVE_CURRENT you need also some additions in language part. But the first line is not necessary.
msl