Possible to Continue Serving Expired Objects When Source Becomes Unavailable?

[Tim McNerney <mumbly@xxxxxxxxxxx>]

Is it possible to configure Squid so that if an object becomes stale  
and the server tries to fetch a current copy of the object, but the  
object/server is unavailable, it will continue serving the cached  
version?

If so, what other control can be used in this case? Say you want to  
allow it to run an hour over expiration before purging it. Or you  
wanted to set how often to retry the source server.

This question is specifically for 2.6, but it would be great to know  
if things have changed with newer versions.

Thanks.

--Tim