Freebsd-update and update of jails

[Patrick Lamaizière]

EHLO,

Is there a way to use freebsd-update and use it to update the main host and 
serveral jails ?

To update my jails (from the main host) i make a buildworld and then :
mergemaster -p -D /thejail
make installworld DESTDIR=/thejail
mergemaster -D /thejail

How i can use binary update and then update the jails? I would like to avoid 
a make buildworld, so may be i can use freebsd-update for the main host and 
another method for the jails?

(I just discovered freebsd-update, it is cool).

Thanks, regards.