Wan (subinterface) not getting IP from DHCP

Hi guys,

My WAN1 interface has 2 subinterfaces (tagged) connected to my ISP.

One of the subinterfaces must get its IP from DHCP and must send in its DHCP request a class-id ( in Cisco terms: ip dhcp client class-id IPTV_RG and ip dhcp client request classless-static-route)

I can't find anything like that in the fortigate. I've tried set dhcp-client-identifier but it doesnt help.

Is there a way to workaround this? I'm using fortigate 60C running 5.2.14

Hope you guys can help me out on this one.

Thanks in advance.

Cheers Kwanhama