This will a launch a Full Forefront Antivirus Scan on a Remote PC. This custom action requires Sysinternals Psexec to function, which can be downloaded here
PSExecThe custom action is:
cmd.exe /K {actionpath}Psexec \\{computer} "c:\Program Files\Microsoft Forefront\Client Security\Client\Antimalware\mpcmdrun.exe" -Scan -scantype 2
Hope this proves useful for someone!