MultiWan with Vlan

[bohosh]

Hello,
I have this scenario:

ISP router - switch >>>> Vlan switch - Pfsense.

I have only 1 nic free on my pfsense box and this scenario I made to put 4 IP addresses in to 1 Nic on my router. But the problem is that my ISP works with DHCP and I can't get these 4 IP addresses because, my vlan switch has the same MAC addresses on all of its ports. Any Idea how to do that?