All-but-fragment caching suggestion

Hi,

with fragment caching one can cache parts of a page. However, more often
than not what I would need is the exact opposite approach. I would like
to be able to use action cashing and have a mechanism for telling Rails
to exclude one or more areas from the cashing and fill them with dynamic
content instead. A good example would be a page where all content would
be perfectly cachable but one tiny line saying ‘logged in as
[username]’.

Wouldn’t a mechanism for doing this more elegantly be a great addition
to Rails? Or am I missing something and this is in fact currently
possible?

Ingo