Manually Add Sites to Membership

In addition to pages with a specific domain being added to the membership, it would be great to have the ability to manually add pages to the membership without changing the domain.

For example, I have 3 separate products that build on and support one another in my funnel. Product 1 is a low price offer- a weekly newsletter. Customers who purchase product 1 can access it in the membership. Product 2 is a mid-tier product- a course. It builds on product 2 but has its own brand. Customers who purchase product 2 can access it in the membership. Product 3 is a high-ticket offer- a 3-month live program. I often offer products 1 and 2 as a limited time bonus for people who sign up for product 3. Product 3's accompanying material is hosted in the portal. It would be great for each product to maintain it's branding, even in the membership. I'd like the ability to select which pages are in the membership without using one domain.