I have downloaded and installed the morefunc add in and i am currently able
to use the indirect.ext function as required. However, when i send the file
to someone without the morefunc add in, as soon as they open the file it
returns the #name? error in the cells where I have used indirect.ext
(assuming because they don't have the morefunc add in).

Is there a way that the additional function can be attached to the file, so
that the spreadsheet will work when opened by people without the morefunc
add-in. Unfortunately I cannot get everyone at my work to install this add in.