The 'X' button isn't included in the 'buttons' the help is talking about, but this the same for custom /dialog with the 'disable' option. I don't think it would be a good idea to do that though, the feature is meant to prevent misuse of the controls in the dialog, if you mis-close the dialog well, you can always reopen it.
Otherwise, 'bN' to enable the controls after N seconds and enabling ESC to close the dialog are good ideas.
