Security and lp command and -u option

Thu Mar 20 07:16:47 PDT 2008

Hi,
I have a cups server and try to install client (ubuntu feisty).
I have 1500 students using ldap authentication.
lp command has a "-U" option to specify USERNAME.
but if a student, username "student1" type "lp -U student2 file"
it prints "file" using the "student2" account.
I also use pykota for printing quotas and the command use the student2 quota.
I don't know how to block "-U" option to prevent users to steal quota from others !
Do you have any idea ?