If you code it properly, you can monitor for key 5 by scriptmenuresponse. Simply add it in your menu file:
Code:
execKey "5" { scriptmenuresponse "5" }
which will show in _menus.gsc as:
Code:
if( response == "5" )
self thread yourfunction();
Is it possible to bind 5 not to open the menu
but it is obvious when you're in the game
For example, while you're in the game you push the button 5 and then you set sentrygun