asterisk users - Jun 2007 - ENUMLOOKUP well succeeded but callee server unreached

I use ENUM lookup in my dialplan before sending calls through my PSTN trunk.
One problem arises... When ENUMLOOKUP finds an SIP contact for that e164 
number, Asterisk dials that contact, but when the remote server that 
should answer the call is down, or the IP link is down for some reason, 
the dial to PSTN trunk (which has the next priority) only takes place 
after the ring time of Dial application has expired (although it didn't 
even ring, but Asterisk keeps sending INVITEs to the callee server until 
Dial timeout).

Is there any way I can force my dialplan to skip to the next priority in 
a few seconds (dialing my PSTN trunk) if there is no response from the 
callee server at the INVITEs sent my my server?

Regards,
Ricardo.