Configuration BT home and pi

I have got BT router with openwrt dual wifi, and raspberry pi. I would like to use Bt Router wifi-AC to connect to source of internet and say wan port set for bridge- connect from BT Wan to rasberry LAN- rasberry as a router. And I would like to use the same lan cable (betwen bt and rasbery) and send internet throught pi lan to Bt lan and from Bt lan to wifi N. So Bt Ac radio would work as a client. Bt N use as a access point. Rasberry pi use as a router. The only problem is there is only one cable that connect pi and BT. Is it possible to set it up ?