asterisk users - Jan 2005 - Can Asterisk generate a 404 message back to a UA?

I've got the following situation where a UA is trying to call another UA via
Asterisk and SER according to UA1 -> * -> SER -> UA2.  Now in the event
that
SER generates a 404 Not Found for UA2 I would like Asterisk to return or
relay or forward or whatever the 404 to UA1.  Anyone know this might be able
to be done (or maybe not possible at all?)

Craig