I have a spreadsheet that has a number of calls to functions that are
contained in an add-in. My users start up the spreadsheet by browsing to the
directory and double-clicking the .xls file. They fill in financial
information, then save the file under a different name. So the original file
is really just a read-only template. What I want to happen is that whenever
they open the template file, or any of the modified files, it will check to
see if the addin is loaded and, if not, load it. For various reasons I don't
really want the add-in loaded permanently; just when one of these
spreadsheets is opened.

I've tried putting the code in the workbook_open event of the spreadsheet
that seems to load the add-in when necessary, but the functions still don't
work (#Name). It works fine if I load the add-in first, then open the
spreadsheet, but this is not agreeable to my users.

Any ideas? Is there a different event that I should use? Or perhaps a
different strategy altogether?