I don't think WMI/ADSI provide that information remotely.

You could script some stuff together to get that information
if you really had to, but not sure it's really worth the
time to do or not. Guess you'd have to decide that.

First check if someone is logged on
If they are then you could use their SID and check here

$sComputer = 'system name'
$LogonServer = ReadValue($sComputer+'HKEY_USERS\their SID\Volatile Environment','LOGONSERVER')

You could also use the RemoteExec UDF and have it launch
on the remote system, read the environment, write to a file
then you read that file, etc...