Bob,
I found the following link at IBM,
http://www.ibm.com/developerworks/aix/library/au-settingupchroot/index.html
This does take a bit of work it seems, not simple as you might want.
Why not have the users deposit the files on another system and once they log off kick off a process to sweep the files if any, check them and then copy/ftp where you want them?
Hope that helps
James
