Multiple WAN IPs single physical interface

[silverhoof]

so very simple concept. i want to take the single 2.5gb connection from my isp docsis modem (Shaw/comcast XB7) and connect it directly to my firewall AND pass all 3 ips to the firewall with ought using multiple connections or a switch in-between. these ips unfortunately roll so using static virtual ips is not much of an option. it must be able to get the 3 ips using dhcp. does this seem possible?
what i would want would be the ability to attach a physical interface into a vswitch and use internal virtual interfaces. i want to avoid using my proxmox VE server and keep this on bare metal.
equipment in use:
Comcast XB7
Checkpoint PB-20 i7-4790 16GB Ram with 4 port 10gb sfp expansion