That's purely a Tk question. I think there is no way to do this, but
Tk menus have a "tear-off" feature which you can use to keep a menu
posted for a longer period. I forget how to invoke it, but it's
something like middle button drag.
--Guido van Rossum, CWI, Amsterdam <mailto:Guido.van.Rossum@cwi.nl>
<http://www.cwi.nl/cwi/people/Guido.van.Rossum.html>