That is what the -command parameter of Button is for. So, construct your button thus:

$angel = $MW->Button(
  -text    => 'Launch Scripts',
  -command => sub { 
      print STDERR "Launching..."; 
      system("./scriptname"); 
  },
); ##not sure why you're using exit, so I left it out.
[download]

That will run ./scriptname on every button press.