After staggering through Mastering Perl/Tk, I come up with this, which seems to work:

 my $fm = $menubar->entrycget('File', -menu);
# *after* creating the File Menubutton in the $menubar

sub select_file { $fm->entryconfigure('Edit', -state=>'normal') }
[download]

--Bob Niederman, http://bob-n.com