You can "add" an email attachment by entering the unique email URL into the description of your event. The URLs will look similar to:
The next time you open the event, you can click on the hyperlink, and it will take you to your email, where you can review your attachment.
(I wrote the St. Olaf FAQ entry, so am plagiarizing myself :) Or not, if there is a better way :)) )
With a little side of applesauce...
©2006 Shannon Eric Peevey