A transport rule will help. See this
Technet article, specifically the Apply a disclaimer to the message
sections. The downside is that by default - without any custom scripting, or exceptions to the rule so that it doesn't apply if it encounters the same text - this will be appended automatically, without regard to whether it was present already. So what you'll
end up with, considering a scenario when you're exchanging 5 sets of replies with an outside party, is a message that has embedded 5 map links. However for meeting requests this shouldn't be the case, since usually there's only the original mail + accepts/rejects
as replies.
If you really want to prevent the disadvantage listed above to greater extent, either a 3rd party product or
writing your own custom transport agent should do. It's up to you if it's worth the effort.