The answer is: best not. You can always provide a Web frontend to allow database access while limiting the options a user has with YOUR code.
If you really have to create a guest account with (hopefully) limited rights, you could try the PhpMySql frontend. if you can't do it there, it will be due to security restrictions.
If you could give a more precise idea for what purpose you need the guest account, maybe there are different approaches than a passwordless DB access.
Regards, Stefan