I think you have the idea of the mirror slightly wrong.
I do have a mirror working. And yes, I can log into the console on the mirror, but here is the really big but, you should never log into the console on the slave as if you make changes, the master will be out of sync. This is why the guide says not to install the console on the slave.
The idea of the mirror is supposed to act as a mirror server not mirror ispconfig console.
A better way to think of it is to think bigger. You have one ispconfig control panel server and a load of other servers being controlled as slaves. Some of those slaves may be mirrors of each other. If one goes down the other can stil be used if you adjust some ip settings.
If the control panel server goes down, never mind. The other slaves don't need a master to function.
If you want to make a backup master that's a different story.
When Falko talks about a failover ip there are tutorials to help you achieve a system where a second server will take over the services if the first fails.
Hope this helps - unless I have the concept all wrong myself!
in which case we're all in trouble !