I don't think it's possible. The d-link device contains components (dhcp client, dns client etc) which will look to its own WAN port. But you can't use its WAN port as this is linked to its internal modem and is exposed to the outside world via the ADSL interface.
It is possible to use some routers as switches, by using only its LAN connections, but you lose any firewalling capabilities it has. You do also need some routing capability to link your LAN to the WAN, and I don't know if the cable modem (a genuine modem is not a router, but some so-called modems are in fact routers.

) does this. The d-link using only its LAN connectors won't either.
Home gateway devices come in two flavours - "adsl" and "cable/dsl". You need the second sort, but you have the first sort.
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http://www.vfast.co.uk/ - 2 Mbps symmetrical via fixed-link wireless