[Pan-users] Invert selection in headers list?

[clarjon1]

Hi there.
Is there an option/command to invert the selection in the headers pane?
I'd like this so that I can, when i'm mass-caching messages to read
offline, filter out uncached messages, select all cached, remove
cached-only filter, then invert so that only uncached messages are
selected.

I'd appreciate being able to do this because in some of my subscribed
groups, slecting all headers and then telling it to cache will cause
it to lock up for a few minutes, for whatever reason, before beginning
the download.  I suspect it may be deciding, message by message, which
ones to download, as the waittime grows the more messages I have
already cached.

If this isn't possible, perhaps a filter button which is the inverse
of "Show only cached" might be available?

Thanks in advance for any input/suggestions.

-- 
Jon