How do you use external files as if they were #included?

I understand the basics of OOP and classes, but I can’t seem to find an answer to something between classes and static functions.

For instance, what if I have a Game.as class that’s 1,500 lines long and I want to yank out groups of functions into external files (such as Scrolling.as or DepthManager.as)? Classes don’t seem quite right, since I’m dealing mainly with the Game class variables, not separate entities. And putting one function per file would create so many dang files it’s arguably worse.

So is there a way to do something like the old #include directive that will tell my Game.as class to just insert the contents of certain files into the middle of the Game.as class so I don’t have to monkey with MovieClip(parents) and debugging the theoretical paths of null-object errors?

I’m guessing they took away #include for a reason, but I’m going to wear out my scroll wheel if I don’t find a solution soon…

Thanks in advance for any help.