Need my router (RT-AC66U) as both repeater and switch

So I just moved to a new rental and I am getting my internet from the owners WIFI upstairs. Due to the low signal strength I have been forced to use my Asus RT-AC66U router as a repeater to have usable signal in the apartment. That is a problem as it locks out the use of the LAN ports so I cant hook up my TV, server and gaming rig. So now I am looking for a solution to have it all up and running again without large investments in new gear or reconfigure of already setup hardware (mainly the server since changing the IP is said to be a pain).

Is there a option that I am overlooking/not finding that lets me use the LAN ports as a switch (with IP 192.168.1.***) but still getting the connection to the internet through WIFI while it is still working as a repeater? I am totally open to flashing the router to dd-wrt or tomato if that helps me reach my goal although I have no experience.