BACKUP DATABASE and BACKUP LOG permissions default to members of the sysadmin fixed server role and the db_owner and db_backupoperator fixed database roles.
If not you could take advantage to EXECUTE AS in this case.
thanks Satya. I was hoping in SQL 2005, may be they had come up with something better. The only problem with db_backupoperator approach is that every time you add a new database to the server, thethe id needs to be given access to that database.