Accessing Function on Sub Class via Default Class

I’m trying to do this,

Main.instance.subClassFunction();

instance is a public static variable on the default class, Main.

I can do Main.instance.defaultClassFunction() with no problems at all, I use it to access functions and variables from within other classes.

Is it possible to use this method to call a function on the subclass, currently I have to do this,

Main.instance["subClassFunction"]();

I think that’s too messy and would like to know how to get around this. I have tried doing this:

Subclass.instance.subClassFunction();

But it throws an error, 1119: Access of possibly undefined function…

I can also do this,

var ins:Subclass;
ins = Main.instance as Subclass;
ins.subClassFunction();

But again, messy.

Can anyone help?