managing multiple sites with common functionality

[SebastianRoberts]

Hi,
  I've created a public web app based on the sample flex viewer.  We would like to create an internal web app with much of the same functionality, but some additions and changes.  Does anyone have any suggestions/ papers / links specific to flex (and ideally the sample viewer)  that might help me manage this most efficiently?
  I know well enough not to just make a copy of the project, and maintain 2 similar code bases, but there is surely a better way to go about it other than have a global variable and a lot of conditionals buried all over the place in the actionscript code-

if (public) then .... else ....

Thanks,
Sebastian Roberts
Nevada County GIS