It's been a personal peeve of mine that Aladdin makes a CLI interface to their product for Linux, but not for the Mac. Here is a quick alias to fix this. It's not perfect (if you aren't logged in, this will have problems), but it works. The command to create the alias is:
alias unstuff "open -a '/Applications/StuffIt Lite 6.5/StuffIt Expander.app'"(your path to StuffIt Expander might be different)
Mac OS X Hints
http://hints.macworld.com/article.php?story=20011021164025306