Membership and Pro Sites plugins working together

I have Membership and Pro Sites plugins installed in a Multisite network. With Pro Sites I want users to be able to "purchase" their own blog at the network, but I want them to also become members in the main network site that includes a blog. I want those users to be able to access the full posts in the blog of the main network site.

Is there a way to do that automatically with the functionality provided by those two plugins, or I would need to develop something custom. If that is so, could you please point me in the right direction about what I would have to do?

Thank you.