order += "external_script foo"                                                           
order += "external_script bar"

external_script foo {                                                                      
    format = "{output}"                                                                        
    script_path = "/path/to/foo tray"                              
    cache_timeout = 15                                                                       
}

external_script bar {                                                                      
    format = "{output}"                                                                        
    script_path = "/path/to/bar tray"                              
    cache_timeout = 15                                                                       
}