I just need to create a windows system environment variable sql_backup_drive="X:\" for each SQL server and use it to determine the location of backup folder for each server in a multiserver job. I planned to use "subst" command for it, but it works really bad, if MSSQLSERVER service uses a domain account.

Of all extended procedures, only xp_cmdshell seems to be able to fetch a windows system environment variable into stored procedure variable, but still I did not found how to do this...