No, since it would defeat the purpose of user account protection on a multi-user system. If you enabled guest accounts, those guests would be able to fast-user-switch into your account, FileVault accounts would break, etc.
As far as I know, it's possible to set an Open Firmware Password using a utility on the OS X DVD, but this only applies for non-default boot options (boot into Bootcamp, boot into single-user mode). (article currently in maintenance, see Google cached copy)
You could set up the username/password login screen instead of the list of users, and use nonobvious user names as "subsitute passwords". If you select the user name from the menubar icon, you are logged in/switched immediately. This is a really stupid idea from a security point of view, but it's the closest possible "solution".