Using AndroidJavaProxy with abstract class

I'm trying to use AndroidJavaProxy to implement an abstract class, but it always gives me an error and will only let me implement interfaces. Is there any way I can implement an abstract android class in c# only

My goal in the end is implementing some abstract classes from the PebbleKit android tools so I can control my game with a pebble smartwatch. Ideally, I'd only need to include the pebblekit jar and my c# script without having to write my own android classes as glue. If I've got to write android classes so be it, but I think it's simpler if I can just implement an android abstract class in my c# script.