Start by creating a new user in the Accounts System Preferences panel. It doesnt really matter what name or access level you give the new account; its going to have a very short existence. Once the account is created, move the troublesome file from the trash into the /Users/Shared folder. Now (via Fast User Switching or a traditional logout/login), log in as the new user. Open the /Users/Shared folder, and move the troublesome file into the new users trash.
Now logout of the new account and log back into your main account. Return to the Accounts pane in System Preferences, select the account you just created, and click the minus sign (or just hit Delete). The system will put up a dialog box asking if youre sure you want to do this, with three options: Cancel, OK, and Delete Immediately. Select Delete Immediately, and the troublesome file (along with the new user and the disk space they used) will disappear. (If you just press OK, the files from the deleted user will still reside on your drive.)
