Constrain a Sprite's Parameter to a Global Variable

What I'm trying to do is super simple...yet I can't seem to find a way to do it. I simply want an actor's parameters to be tied directly to a Global Variable. Like, being able to simply type the name of a global variable into the parameter field. Is this not possible? Do I need to play "tag back" and just have the game constantly pushing the variable value to the object?

The objects have instance variables, you can use global variables for more general things like player hp or score.