J-BusinessDirectory - Special premium package for members of an non-pofit association

Hello everyone, I am looking for a workaround or solution for a complex problem. I hope you have better ideas than me 

I am supporting a client who wants to operate the JBusiness Directory. However, the client is a non-profit association in Germany and wants to offer its institutional members benefits in the directory through a premium package. This premium package should not be purchasable but exclusively available to institutional members (for free). All other users (non-members) should still be able to use a standard entry for free.

Unfortunately, I can't find a good configuration to implement this properly. If I specify that both packages (Standard / Premium) are free, anyone can independently upgrade a standard entry to a premium entry at any time, even if they are no institutional members. This is not desired. Premium entries should alsways be manually reviewed and approved by us.

Then I thought: OK, I'll set a price and offer members the option to receive a 100% coupon. However, if I define a price for the premium package, everybody wether they are a member or not, can register for the premium package, is asked for a payment and an invoice will be generated. This is also not desired because:

1. We only want to offer the premium package to members. It must not be purchasable by non-members, and
2. Users are either already institutional members and therefore do not need to make any additional payments, or they apply for institutional membership – but this application/payment does not take place through the directory. Conclusion: Setting a price does not work either.

Setting up the premium package that it is only visible to admins partially solves the problem; however, no one can apply for a premium package since it is no longer visible in the frontend. My current idea of a workaround would be to only offer the standard package to all and to set up an extra form with which institutional members can apply for a premium upgrade (which we would manually check and approve). But this solution would be not very comfortable...

Another option would be to configure that every item has to be reviewed. However, we would then have to regularly check everything, which we also don't want. The solution using a threshold unfortunately doesn't help either because once the threshold is reached, it would again be possible for someone to independently switch to the premium package.

Does anyone have an idea for a better solution/workaround?

You can also use the user groups to filter the packages that are being displayed. You can create a package that is available only for institutional users.
Would this be an option for you?