Outliner create slice group via API, somebody can help?

Either you will need to determine the ID at the beginning of each session (or just before using it) …

… or you could use WIN32OLE and the SendKeys() method.

  WIN ||= Sketchup::platform == :platform_win rescue RUBY_PLATFORM !~ /darwin/i
  require 'win32ole' if WIN

  def group_from_slice
    if WIN
      WIN32OLE::new('WScript.Shell').SendKeys('{ESC}^%s')
    else
      puts "Feature is PC Only"
    end
  end

I send the ESC key to close the Ruby console window, so that the
main application window will receive the CTRL+ALT+S keystroke.