You can use mouseover, mousein, and mouseout in mirc. It's true that it's a little more trouble than those specific commands, but it is not that difficult to do (and you could easily script an alias to make those specific commands).
Use $mouse which can allow you to find out if the mouse is in a specific location (rectangle) which can be used for all those commands. Many scripts make use of this command and have notes appear in their dialogs based on what the mouse is over.
