There are several ways to remotely create environment variables (adm templates, loginscript, group policy preferences..)
The quick and dirty way is to open a remote registry and create the environment var key:
Open Regedit – File – Connect network registry. And fill in the remote computername:
Browse to Environment in the HKLM hive:
Create a new String Value. Give it a name and fill in the value.
After rebooting the machine, check the system environment vars on the client machine: