Some copy here explaining how people can join / the process...
You can link to an XL file in the copy by copying it's url (after you have added it below the body) and linking to to it like this
Then you can un-check "DISPLAY" next to the file if you don't want it to show below the body in the list of files.
If you chose not to DISPLAY any files then the section below the body will not show up on the page.