A while ago I've written a patch to qjackctl which adds DBUS support to start and stop the JACK audio server. It's available and enabled by default in qjackctl from version 0.3.4.11 upwards.
The main use-case for it is to bring up the JACK server after a suspend/resume cycle on laptops. More information about this is available on a Wiki Page. This blog will just give minimal usage information to tease you :)
An example script to re-launch JACK with the last chosen preset looks like this:
/etc/pm/sleep.d/90qjackctl.sh
#!/bin/bash
case $1 in
thaw|resume)
(sleep 4 ; dbus-send --system /org/rncbc/qjackctl org.rncbc.qjackctl.start)&
;;
*)
;;
esac