It might sound obvious, but how about starting the app, then withdrawing the mainwindow to an icon? From the end users point of view, he clicks the icon, and the program comes up immediately. The only drawback is it uses some cpu while it sits there, but you could probably work out a scheme to put some "sleep" into it. Maybe let it sleep while it's iconified, and have it fully awake when it's deiconified?

You probably need to intercept the window manager's close command..

#prevents mw from closing and iconifies instead
$mw->protocol('WM_DELETE_WINDOW' => sub {  $mw->iconify });
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For sleep, maybe something like this

tksleep($mw, 100);

sub tksleep { 
  # Like sleep, but actually allows the display to be 
  # updated, and takes milliseconds instead of seconds. 
   my $mw = shift; 
   my $ms = shift; 
   my $flag = 0; 
 
   $mw->after($ms, sub { $flag++ }); 
   $mw->waitVariable(\$flag); 
}
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