Unfortunately it's currently not possible to get multiple dynamic public IPs per DHCP.
With 2.0 where CARPdev is used it "should" work.
A possible (ugly) workaround:
Plug as many NICs as you have additional IPs into your pfSense and set them as DHCP.
Like this your additional NICs will request an IP from your ISP.
Another (similarly ugly) workaround would be to connect a VLAN capable switch to your pfSense and assign as many VLAN-interfaces as you have additional IPs.
You would need to assign a PVID on the switch for each "virtual" interface and then connect them to another switch which then goes to your modem/router/whatever_connects_you_to_your_ISP. (you need a separate cable for each virtual interface from the VLAN switch to the normal switch).
This would look like this:
pfSense
|
|
VLAN-switch
| | | | | | |
normal switch
|
|
modem