Since powerline network is already working for you, what you need is an powerline networking unit that bridges to the WiFi signal at the far end of the building. Something like this TP Link TL-WPA281 AV200 Powerline Extender with Wireless N Access Point or one of the many others like it in the PowerLAN category. This adapter creates a WiFi hotspot at the outlet of your choice, and backhauls the traffic over the powerline through another adapter to your internet access device.

Ideally you want to match the powerline network technology version and possibly the maker for compatibility. If your existing powerline network adapters are much older and slower, you might as well get a new set. The current speeds are 200 Mbps and 500 Mbps.

Setup the powerline WiFi access point on the powerline adapter with the same SSID and key, but on different non-overlapping channels.