If your ISP can only provide those IPs to you directly on the WAN, rather then routing them to you via a different public IP, then your options are limited.
You can setup IPAliases for those publlic IPs on the WAN connection and then 1:1 NAT them to private IPs internally. That means the servers using them cannot have a public IP directly which may or may not be an issue.
With a non-PPPoE connection you could bridge the WAN and the internal interface in order to use the public IPs directly on the servers.
Steve