There was a transclude plug-in (never used it myself though) and you could try it by accessing the old screwturn site using web archive at:
http://www.screwturn.eu/Customize.Transclude-Files-Plugin.ashx
The markup instructions are on this page:
http://fiala.cc/ScrewTurnWiki.Transclude-Files.ashx
And lastly, to download the plugin:
Bear in mind that the plugin was for an older version of screwturn but I generally found them to be forward compatible. Its worth a shot! May want to try on a test install of screwturn through. No warranties! :)