Another work around would be to add prop2 and declare it as undefined, then add a setProp function on your object that can set the property for you.
var obj = {
prop1: {someValues: [], someValue: {}},
prop2: undefined,
setProp2: function(){
this.prop2 = this.prop1;
}
};
Maybe it is possible for you to make a small function that makes an instance of the object and calls the setProp2?
Not sure this is what you are after. If you can supply what you want to use it for then it might be easier to supply a different approach.