Set %var as a global variable when it gets declared (e.g. $var = %var;) and use this loop to continue checking for it until it exists.
function checkVar()
{
     if($var !$= "")
     {
          $var2 = getWord($var,0);
     }
     else
     {
          $var2sched = schedule(100,0,"checkVar");
     }
}
You can use cancel($var2sched); if it never finds a result for $var.