Download nuget package without project with the dotnet cli

Question

Given the following file packages.config:

<packages>
  <package id="package.a" version="X.Y.Z" />
  <package id="package.b" version="A.B.C" />
</packages>

I used to run the following command:

nuget.exe restore .\packages.config -PackagesDirectory .\Dependencies

That downloads the specified packages into the Dependencies folder without having a csproj file.

I am looking for a way to do the same with the dotnet cli (because I need it to run on non-windows environment), but I can't find how.

I tried several things without success:

dotnet restore --config-file .\packages.config --packages dependencies
dotnet restore .\packages.config --packages dependencies
dotnet nuget restore .\packages.config -PackagesDirectory .\dependencies\

The closest I can get was by replacing my old packages.config with a project file with PackageReference (I named it dependencies.config):

<?xml version="1.0"?>
<Project Sdk="Microsoft.NET.Sdk">

    <PropertyGroup>
        <TargetFramework>netstandard2.0</TargetFramework>
    </PropertyGroup>

    <ItemGroup>
        <PackageReference Include="package.a" Version="x.y.z" />
    </ItemGroup>

</Project>`

And running the following command:

dotnet restore .\dependencies.config --packages .\dependencies\ 

But doing so, I have to specify a TargetFramework property and the command automatically download some other packages (microsoft.netcore.platforms and netstandard.library). I can live with that but I would like to know if I was missing something.