This is not really a KiX question unless you are looking for an alternative to NET SEND. NO amount of scripting will change the behavior and limitations of NET SEND.
Quote:

C:\>net send /?
The syntax of this command is:


NET SEND
{name | * | /DOMAIN[:name] | /USERS} message


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Give a man a fish and he will be back for more. Slap him with a fish and he will go away forever.