DDX / DDY on Android

Hi all,

I am trying to achieve flat shading with the below material:

This has worked great on PC but when I try to make it for mobile the engine tells me that DDX and DDY are not available on ES2. I think this is because they are GPU features (but that is beside the point). I have looked around a bit and found a number of people asking for a mobile equivalent but have not found a good solution yet.

Does anyone know of an alternvite to DDX/DDY flat shading on Android devices. I am currently using a Nexus 5X.