Pro Sites Quota Limit For Free Users

Pro Sites has a built-in, "Free" level by default.

Using Pro Site's quotas, you can place limits on the number of posts members can make.
(/wp-admin/network/admin.php?page=psts-settings)

You can place different limits for different Pro Site Levels, however, you can not place limits on the built-in Free level account.

How can I limit the Free level? I want to allow the Free member to post no more than 3 posts.

I found a similar request from 2 years ago:
https://premium.wpmudev.org/forums/topic/is-free-quota-limit