I realize it's bad form for me to ask a question in response to a question, so please forgive me, but... what benefit do you hope to get by embedding a non-Tk GUI (which you create) inside a widget of a Perl-Tk program?

Is your non-Tk GUI set up so it can also work by itself (not inside a Tk widget)? If so, and you are looking for a way to make its output accessible to an "outer" Perl-Tk GUI, why not run the "inner" GUI as a pipeline file handle

open(MYGUI,"inner-gui |");

then setup a

Tk::Event->fileevent

for that file handle? This would seem to keep everything simpler, and might perform better -- both GUI's do their normal thing, both are handled by the main window manager.

If do have a compelling reason for the "embedded GUI apps" approach, I'd be very interested to learn more about that sort of situation.