Cache parts of pages?

[Kai Grossjohann]

Our web site has a navigation bar on every page with a picture of the
day in it.  Let's say that most pages never change after being created,
except for the navigation bar.

Is it possible to use Varnish in such a way that the "meat" of every
page is cached separately from the navbar, and on every request the
navbar is merged into the "meat" of the page just prior to delivery?

Idea: Have Apache deliver a page with server side include instructions
in it (to include the navbar).  Then have Varnish cache those pages.
Have another Apache in front of Varnish that interprets the SSI
instructions.  I have no idea how to configure the second Apache,
though.  Furthermore, this is very kludgy.  But I hope it illustrates
what I want.

Ideas?

Kai