Should also mention you have the option on the pull window to "pull this target".
In other words pull up the map, right click on X mob to target, then click "pull this target " to have RGMercs path to target, aggro, and run back.
I am.sure there is line code to make a hotbutton for it, I have been using the UI button when I want to selectively auto pull.
At work, so I may have the exact wording wrong of the button.