I have a Netvanta 3140 connected to an ISP that has allotted me a /27 subnet. I currently have that working and have some servers running behind NAT with the first four public IP address mapped to those servers. Everything is working OK right now. The WAN is on giga-eth 0/3....
Gig 0/3 connects to your ISP? Is this the /27 subnet, or did they route the /27 to you via a /30 that's native on gig 0/3?
If the /27 is routed to gig 0/3 then make a VLAN interface for it, and configure gig 0/2 and 0/3 to be access ports in that VLAN. They'll just bridge. Use an IP within that range for your public host, with the /27 mask and your ISP's gateway.
If the ISP is using a /30 as the link to you and the /27 has no physical interface then configure gig 0/2 as the /27 subnet or DMZ. Keep your existing NAT policies, assign an IP within the /27 as the host and use the IP on gig 0/2 as its gateway. Create access-policies for it to route to the ISP and vice-versa.