I have no idea if it's of use in your situation, as I've never used it myself, but both the "wish" program and the [toplevel] command have a -use option for embedding the toplevel (. in the case of wish) in another window which is set to be used as a container. This can be another Tk toplevel (with -container given), but can also be a window in another app, as long as it's set up for embedding and you have the appropriate id to pass to -use.