I'm aware of no such limitation. Would you mind sharing what lead you to "realize" this?
Paste the following into a file named message.bat.
net send %1 "Good Morning."
net send %1 "And"
net send %1 "Just"
net send %1 "in"
net send %1 "case"
net send %1 "I"
net send %1 "dont"
net send %1 "see"
net send %1 "you"
net send %1 "again,"
net send %1 "Good"
net send %1 "Afternoon,"
net send %1 "Good"
net send %1 "Evening,"
net send %1 "and"
net send %1 "Good"
net send %1 "Night!"
Then from the command line, call it like so:
message.bat YourUser Jon Hawkins