Using a global search and replace worked for me in Word XP:

Make sure your Endnote Reference style is NOT set to "automatically
update".  Select all of the text, but not the endnotes at the bottom.
Click on Edit | Replace.

In the "Find what" box, click on Special | Any character | Format |
Style | Endnote Reference.

In the "Replace with" box, click on Special | Find what text | Format |
Font | Hidden.

Replace all.