First you need determine which users you want move, for example you need know channels names.
After that you can use
ChannelRedirect(${CHANNELNAME},conference_context,${CONFNO},1)
Which will move user to extension ${CONFNO} in conference_context. In that context you need have something like
[conference_context]
exten => _X.,1,Meetme(${EXTEN},d)
Unfortanly no easy way select CHANNELNAME via dialplan. It will require some very complex context which require guru level to create. You can't move user by it number in conference(becuase no numbers).