How to bulk add members?

I just started using Protected Content and it seems like there's no way to add a bulk of wordpress-users as members. In my installation there are more than 6000 users with a certain role that I need to add as members. I'm not so keen on adding them one by one :wink:

Is there a way to do that in a bulk? For the moment it would be enough to get a hint, how I could do that with a script.

Thanks for your help!