'Referring to Variable' question

Hey guys, i made a trigger where when a player selects a hero it adds that hero to a variable (Unit-type variable)
What i need is for the trigger
'Unit - Issue Order With No Target' to refer to my variable to make the unit stop, but it only lets me choose from units already placed on the map. Is it possible (without jass) to make it refer to my variable cus if not then im fudged :(

set MyUnit = random unit from unit-group HeroGoesHereWhenSelected


Or, when you select the unit, add it to a unit variable instead of a unit-type variable, so you can just use that.