I do believe that this is possible, but not very easy.
it would take a good rewrite of the script.
This limit has more to do with the HTML then the fancybox.
In HTML each document window is its own entity with no knowledge of
other windows.
essentially you want each window to be aware of the other windows.
In order to do that you must have a "hook" via JS for every window,
AND every window must have its own JS file that tells it which file it
is and references the other windows JS hooks.
There is no way the developer can do this for you, it is a custom
solution based on your needs.
And a lot of work, if you want to do it have fun, and feel free to
post the results here!
It is possible to open a fancybox in a fancybox, just make the first
one and iframe and include the fancybox script in the iframe source.
Just make sure your second fancybox is smaller because it is now
limited by the size of the window, which is the size of the open
fancybox.
You may be able to use it like this and use the target command, or JS
equivalent, to reference the root window, and exit both windows.