Two ways to serve up static files that are not in the context of the controller.xql:

if (contains($currentUri, 'pix/')) then 
    <dispatch xmlns="http://exist.sourceforge.net/NS/exist">
    	<forward absolute="no" url="{concat('/../data/pix/', $exist:resource)}"/>
    </dispatch>

if (contains($currentUri, 'graphics/')) then 
    <dispatch xmlns="http://exist.sourceforge.net/NS/exist">
    	<forward absolute="yes" url="{concat('/rest/db/data/graphics/', substring-after($currentUri, 'graphics/'))}"/>
    </dispatch>
    

This is commonly used when e.g. the site logic and controller are in /db//site (which may be mapped to a subdomain), controlled by admin, while the content needs to be controllable by editors (so it's in e.g. a /db/data). I've had to re-figure this out a couple of times, so I'm blogging it for future reference.