Spoof WiFi settings as 'On' but use Cellular Data (for specific apps or in total)
In order to simulate a wifi connection on 3g/4g (assuming you are rooted), you additionally need Xposed framework installed and install Hack connectivity service tool.

You then choose wifi and activate traces

See below:



This module forces the Connectivity manager  to return Wi-Fi networking info as active.

An alternative tool (if Hack connectivity service module is not working) is Fake Wi-Fi Connection module try v1.9 (beta) for lollipop+. Sometimes some applications won't work when no Wi-Fi is detected so it simulates  an active Wi-Fi connection in order for apps to get internet. It uses the same concept as the above tool.

Edit:

Another suggested option is to decompile the apk file and make 


  network connectivity check always return true.


Hope this helps