You could create a custom directory, but that would go against the licensing terms. I suggest you check your expected setup with Qlik or with your Qlik partner for a better usage of your license capacity.
Custom directory is only for users you create, you will need to maintain that table for every user you have to add or remove, change passwords, modify, etc. These cannot be mapped to actual accounts in Active Directory or any other directory for that matter.
Also, depending on which version you run of QlikView, the quarantine period will apply even if you delete the user.
There are several things I would like to mention here:
Think of custom users as an "experimental" feature, they are not meant for production. Check with Qlik Support how they are supported.
From the security standpoint, custom users are weaker than any other method. You can apply section access, but the permissions in the folders still need to be set up in the operating system.
Same applies to web security, depending on your network setup, those users will need to have access to the web server, proxies, etc. Since those are not "real" users, you may need to still use valid user accounts.
Custom users can degrade performance if you use more than a few, since they are stored and handled by QlikView in text (XML) files.
You seriously need to think if you want to contravene the license agreement.
I don't recommend the use of custom users, nor I see the need or benefit, other than experimenting with the product or learning.