learned sth about IPoE after captured some pkts via port mirroring from IPTV device. so the next might be: assign static IP & MWAN3(src/dst ip), igmpproxy(udpxy optional), and fake DHCP options on IPTV WAN.
openwrt udhcpc -x 0xHEX:VAL is useful on this case, but there's report say tx id in dhcp packets can be used to calc option data. so the answer would be using a static txid (so that is the same as replay attack!)