How to add a Project (.csproj) to Solution (.sln) under a Solution Folder using dotnet CLI (command line)?

I am trying to add a csproj to a sln using dotnet sln command line.

Adding the project is easily achievable using the below command.

  dotnet sln todo.sln add todo-app/todo-app.csproj

But how do I add the same under a Solution Folder

As of .NET Core 3 (preview, test with 3.0.100-preview7-X)

dotnet sln solution.sln add --solution-folder foo1\foo2\foo3 bar.csproj

It creates a nested hierarchy as of

solution.sln
|
└───foo1
│   │
│   └───foo2
│       │
│       └───foo3
│            │   bar
│            │   ...