Can the datacenter provider assign a /30 for your WAN interface and route the /27 to it? That'd be a lot cleaner.
Otherwise: from the pfSense book (I hope it's okay to cut and paste small excerpts):
Single IP subnet
With a single public IP subnet, one of the public IPs will be on the upstream router, commonly belonging to your ISP, with one of the IPs assigned as the WAN IP on pfSense. The remaining IPs can be used with either NAT, bridging or a combination of the two. To use them with NAT, add Proxy ARP, IP alias or CARP Virtual IPs. To assign public IPs directly to hosts behind your firewall, you will need a dedicated interface for those hosts that is bridged to WAN. When used with bridging, the hosts with the public IPs directly assigned must use the same default gateway as the WAN of the firewall, the upstream ISP router. This will create difficulties if the hosts with public IPs need to initiate connections to hosts behind other interfaces of your firewall, since the ISP gateway will not route traffic for your internal subnets back to your firewall.