To clarify, what I'm looking to do is on the master, I'd like to have a button on an actionbar I could press that would then trigger the slave to issue a heal on myself (i.e. MT). I was looking for an addon that might do this that I would not have to bind a bunch of keys in order to do...
The trigger and key binds are separate things. The first thing is triggering the action by clicking an action bar button. I'm not an expert on WoW, but I don't think it's possible to make your master WoW control another instance of WoW. because that would allow a huge level of automation and Blizzard would never do it. So you can't really use the action bar button as a trigger. What you have to do is use a third-party program to intercept your physical input event (clicking a mouse button while the mouse cursor is over the action bar button) and have the third-party program carry out the desired action. This doesn't involve any key binding -- it involves writing a script for the third-party program -- and you could just as well tell the third-party program that you want to trigger the action by pressing a key combination. In fact you could do both.

In other words, whether you trigger the event with a key or mouse, nothing needs to be bound because the trigger is seen by the third-party program, not by WoW.

Once the action is triggered, you have a choice of three ways to inject the output into the target WoW. Which one you pick has nothing to do with the way you choose to trigger the action. They are unrelated.

1. Inject a slash command onto the chat line. This is probably a bad idea because it's inefficient and it may violate the rules.

2. Inject a key combination that's bound to a scripted macro. This is probably the best way because it's faster, more reliable, and less likely to violate rules. It requires a single key binding.

3. Inject a simulated mouse click on an action bar button in the target WoW. This is less robust than (2) and also requires a binding.