This DOS script can be used with YAM. 
If in a mail an URL is given , a double click will either open the URL in muiOWB or if it points to a YouTube video, will play it.
I installed it in sys:utilities getvideo drawer. You may have to edit for your system.
.KEY url/A
;called from YAM "on clicking URL"  sys:Utilities/getVideo/PlayYTube %p
set metube `cut  "<url>" char -28`
cd sys:Utilities/getVideo
IF  $metube EQ "http://www.youtube.com/watch"
    ; Requestchoice video  "<url>" ok
    Getvideo.rexx "<url>" play
ELSE
    cd datas:muiowb  ; datas:muiowb/owblauncher does nothing 
    waitforport OWB.1 timeout 0; returns 0 if found ; 5 if not
    IF WARN
        RUN owblauncher 
        waitforport OWB.1 timeout 10
        IF WARN
            echo "waited not long enough or OWBlauncher problem"
        ELSE
            wait 3 ; the rexx command  below will not work without it
            
            RX "address OWB.1 'OPEN  NAME ""<url>"" '"
        ENDIF
    ELSE
        RX "address OWB.1 'OPEN  NAME ""<url>"" '"
    ENDIF
ENDIF
cd sys:Utilities/getVideo
If you solved this in other way would be interested in knowing how