Cache page with dynamic query string

[Travis Crowder]

I am pretty sure the answer to this is: It's not possible; but I am 
hoping to learn something new.

There is a page, let's call it promo.php.  We tell a bunch of people 
about it and append their email address to the page for tracking ... i.e 
promo.php?foo at bar.baz

I believe in other to cache the page, I need to strip the query string 
(since it will be unique).  Is there a way for Varnish to cache this 
page, yet still track the hits?  i.e. Strip the query string for the 
lookup and add it back on delivery.

Thanks,
Travis