It seems that
WMIC only supports jobs created with
WMIC itself or created with the
AT command (source - starting page 205).
That's certainly the reason why you get
No Instance(s) Available.
I am also a Powershell addict, but if it is an issue you could use
schtasks utility (as you mentioned).
To remotely disable a task :
schtasks /change /disable /TN "task name" /S server_fqdn /U domain\user /P password
The advantage of disabling a task is that you are sure that it will continue running until it finishes, in case it was running (only future executions are disabled in that case).
If you want to wait until the task finishes you will have to wait for the process to finish. To avoid the use of another third party tool/command you can do this with
schtasks also, by querying the task status :
schtasks /query /TN "task name" /S server_fqdn /U domain\user /P password | finstr Running
(ps : note that i am not sure about the "running" status because my Windows OS is French. Check this according to your language).
schtasks /END will kill the task immediately.