In Rider, how do I use an .sln file not in the project root folder?

Our code is structured as:

- Readme.md
- deploy.sh
- infrastructure/
-- stacker.yml
-- ...
- backend/
-- backend.sln
-- ...
- frontend/
-- package.json
-- ...

The default behavior when opening a solution is for its folder-view to be rooted in the same folder as the .sln (backend, in this case). Is it possible to either:

• change the root of the folder view, when starting from solution view?
• add solution views from nested folders, when starting from folder view?

• Open Solution Explorer
• Select solution node
• Invoke popup menu and invoke Add -> Attach Folder