Vista Offline Files and Outlook

I'm running Vista Ultimate and Office 2007 on a desktop and latop. I'm using
offline files to sync a number of folders between the 2, with the desktop as
the host, but I work on the laptop most of the time. My question is, is
there a way I can force it to always work offline, unless I manually choose
to work online? The reason is whenever my desktop is available my laptop
will try and sync, but this will invariably fail on at least 1 file, my
Outlook.pst, as I always have at least Outlook open. I'd actually like to
work offline all the time, and manually sync evey now and then when I know I
have all my files closed.

Is there an option/policy/regedit somewhere to achieve this?

Thanks,

Richard