There is currently no way to set solution-wide environment variables as these are set on a project basis.
We have added the NX config file capability beginning with 2.2 update 2 I believe.
If you right-click on a native project and select Add-New Item and then select application config file it will add a file named Application.config to your project. If you right-click on this file and select Edit it will allow you to enter environment variables, COBOL switches and RTS tunables. When you build your application it will copy this file to your output folder as <project-name>.mfgcf. When you start your application this file will be read and the options will be picked up accordingly.
It is possible to add this same Application.config file to your other projects by using Add->Existing item and then navigate to this file and select it. When it is built in the new project it will have the name of the new project with extension mfgcf.
Thanks.