My solution:

    var firstVar  = "one";
    var secondVar = "two";
    var thirdVar  = "three";

    var thisVarHasAReallyLongName       = "four";
    var thisIsAnotherVarWithALongerName = "five";

The different length of the variable names should be derived from the fact that the variables themselves are different. So they should be grouped separately.