Using windows variables (like %USERPROFILE%) in `NuGet.targets`?

Using windows variables (like %USERPROFILE%) in `NuGet.targets`?

The current value of NuGet.exe (command line) (in NuGetToolsPath) is
$(SolutionDir)\.nuget\NuGet.exe
I would like to modify this value to
%USERPROFILE%\AppData\Roaming\NuGet\NuGet.Config
The question is, how to use windows variables in Nuget.targets