Vdom and pppoe single wan isp

hi guys 

i have a PPPOE connection with 5 public ip pool on it connected on a single physical port to a VDSL modem

i want to create 4 more vdoms (other than the ROOT vdom) that each vdom will behave as a separate entity and will have it's own NAT\SSLVPN\IPSEC\MGMT capabilities 

i have no problem create the actual vdom, and no problem creating vlans for LAN interfaces for each vdom

my problem is the wan. i can't figure out how to setup the wan to get my purpose

can it be done?

thank you guys in advance :)

by the way, the fortios is 5.4.3