The <t> line will never fire in a realistic situation. Your target should, in all practical scenarios, have a target, and so either the <tt> line will work on target of target, or the <tt> line will implicit-target heal yourself. The <me> line will also not fire except when out of combat, since when you are in combat you will presumably be targetting something, and therefore the <tt> line will activate.
You're overcomplicating this. Just use <mo> and get used to resting your mouse over your party frame when soloing.