You will not be able to do that with moh in FS. MOH in FS is implemented as
stream, so user don't even have control on which file will start playing
when a caller is placed on hold. That's because a single stream of MOH is
multicasted all the callers that are on hold. To skip to next or previous
song/audio you have to implement your own solution using eventsocket or one
of the many embedded programming languages available on FS.


-- 
Thanks & Regards,
Godson Gera
IVR India <http://godson.in/>