When you describe loading an external file into a variable do you mean loading the actual contents of the file? In which case, see the column about temporary trees in XSLT 2.0 at http://www.xml.com/pub/a/2003/12/03/tr.html.
Yes I do mean loading the content of a file into a variable.
Unfortunately I don't have access to an XSLT 2.0 processor so can't use temporary trees.
I suppose that means I'll just have to do the strip create a new file and then do my other transform on that until I do have access to an XSLT 2.0 processor.