How to use direct delivery before relay?

[Mike Gering]

Is there a way to configure postfix so that it will attempt to use 
direct delivery before relaying to another host?

I've built my webserver on Amazon EC2 which, even with static IP 
addresses, does not handle reverse DNS lookup, causing (relatively few) 
recipient servers reject the mail. We've contracted with a mail relay 
service, but they are more expensive than the EC2 service itself! Since 
we're a municipal government, we need to reduce expenses as much as 
possible. The only solution I can think of is to have postfix attempt to 
deliver outgoing mail directly, and then for failures due to connection 
refusals, deliver them via the relay.

Is there a way to do this? Or maybe there is a better solution. Any help 
is very welcome!

Thanks,
Mike